I will point out that all of the WoW wikis and similar sites are also fan edited. Be cautious what you want to declare canon/non-canon. I want to point out the Pandaren were a joke inclusion and ended up the genesis for one of the most beloved expansions in this game. That Harrison Jones is a parody/homage to Indiana Jones and he was relevant for a while, notably with Cataclysm, and then in Legion, and the Rambo Guy from Redridge who ended up coming back again in Warlords of Draenor, and again in Battle for Azeroth. We’ve had multiple joke characters and questlines that ascended from Meme to actual, legitimate Lore too many times to just wipe it off the board.
The Murloc who we gave the ‘cursed’ weapons that turned the Pirates the Blood-Thane quests revolve around into actual ‘vampires’ is still running around, and has appeared in Legion, the Battle for Azeroth, the Dragonflight Expansion and again in the War Within, acting as an assistant and vendor for Brann and what remains of his expedition.
If Sir Finley Mrrgglton is still running around and is canon to the story on even a tangetial level, odds are those cursed weapons exist as well, and we probably haven’t heard the last of the ‘Vampires’ of Northrend, or their cursed artefacts that can turn any of the Living into more of their accursed kind.
Blizzard has 
-pulled weirder stuff before …
In regards to the vampiric nature, this actually does show up multiple times in the questing experience in Northrend, where Vrykul are capturing living victims to sacrifice to either empower themselves, or to wake up Kin who are still in their ‘stone sleep’. We see this again with the Mogu using ‘anima’, which is a blood-like fluid rich in life force and magical essence that they extract from slaves and prisoners, to fuel their constructs, awaken stone servants and even revive their own dead and fuel the darkest kind of flesh-warping sorcery to attempt to revive their Empire.
Blood Magic has long been in use amongst the Races of WoW, and its not just Trolls, Vrykul and Mogu who practice it. It was often regarded with open hostility and suspicion, and Dalaran quasi-outlawed it because it was too dangerous and had diminishing returns compared to ‘normal’ Sorcery, but it had a level of flexibility and utility that the ‘pure’ Arcane magics lacked, including healing and longevity applications to the caster and their allies. Many Sin’dorei turned to Blood Magic during the reign of Kael’thas and the destruction of the Sunwell because it enabled them to feed on the latent magical energies within all living things to sate their addiction to magic, but most also abandoned it once the Sunwell was renewed because of the dangers inherent in this style of ‘Sorcery’.
In regards to the San’layn as a species or a force within WoW currently, they were very few in number even during Arthas’s reign as the Lich King, and the Murder Hobos Azerothian Florida Man Honster Mumpers Player Characters absolutely shredded the majority of those during their assault on Icecrown Citadel to steal a dead horse from the Lich King. A few would show up again, during the Battle for Azeroth as clandestine allies to the Banshee Queen, but their involvement was short-lived and bitter, as the Alliance murdered most of them and the Horde was quick to oust them again as soon as the Banshee Queen crashed out after getting her receipts called out by Saurfang at the gates of Orgrimmar, and we’ve only encountered a few others running around as individuals, namely in the Sin’dorei Heritage Questline, where a lone San’layn had stolen magical techniques from the Shadowlands to ‘cheat’ Death no matter how many times the Sin’dorei Champion beat him into pavement pulp, and off-hand references to ‘Scourge Warlords’ from the Death Knight NPCs in Shadowlands.
San’layn took a lot of effort to transform, and the only individuals seemingly able to make more with any real efficiency were the Lich King himself, and their dread queen, Blood-Queen Lana’thel, who we re-deaded after some inappropriate biting on her behalf. Its not to say that she couldn’t have been resurrected, given she was a unique San’layn who possessed wings and a vampiric bite that allowed her to grant the same kind of mad blood-thirst that we see displayed by the victims of Blood-Thane Lucard’s ‘curse’ in Legion.
However, in the case of the Blood-Thane, it was his weapons that transmitted the curse, and through that curse, the Blood-Thane Vrykul could manipulate, to a certain degree, those who had plundered his tomb, trying to use them to sate his own need for blood, but he underestimated the frenzy of his ‘spawn’ and they infected, rather than fed on, their fellows and resulted in a massive amount of ‘Vampirates’ running around, affected by the sun, their blood-thirst and the trauma of the influence of the Thane on their minds and generally swinging between bouts of mania, gibbering terror, rare bouts of lucidity where they tried to get rid of the cursed ‘treasure’ and an obsession with staying near the Tomb of the Blood Thane despite having perfectly functional ships with which to sail away at any time.
Assuming there are still San’layn with any real power still left in the setting, they are hamstrung by the fact that, by their very nature, they are Blood Magic users. Its not to say they cannot use other forms of magic given time, training and macguffinite assistance, but their nature as an Undead and one that must feed on blood to sustain their corporeal forms means that every San’layn requires a ‘herd’ of the living to drain from, if not cull periodically to feed and empower themselves. Multiple San’layn without a clear leader and a large stockpile of living servants and slaves to feed on would rapidly come to blows, and few living Sin’dorei or Ren’dorei would willingly undergo whatever ritual that is required to become a San’layn, with the Sunwell restored and Undeath being a torment and a curse, both to the Alliance as a religious issue, and the Horde having had Forsaken as allies for years, and both Mega-Factions having to deal with Death Knights amongst their ranks for years.
That said, San’layn are physically beautiful, powerful, and maintain a strong magical prowess even in Undeath, even if they were not magic-wielders in Life. For an Elf who is dying or who fears death, or whose hunger for power outstrips their fear of damnation or being ostracized, seeking out a San’layn to learn the secrets of the transformation process could be on the books.
Or, more darkly, the San’layn may not know how to make more of themselves. The Lich King obviously knew how, and the Blood-Queen Lana’thel certainly had an infectious bite and enough knowledge of both Blood Magic and Necromancy to resurrect her three strongest lieutenants to fight us in Icecrown Citadel, but the Scourge wasn’t exactly a happy funtime place where everybody got along and worked together. With the Lich King gone and replaced by Bolvar on the Frozen throne, the Blood-Queen smacked like an overfull mosquito and the few Scourge who were able to maintain their free will against Bolvar’s dominion, or who went rogue after the Helm of Domination was disenchanted by Sylvanas, odds are they just ran to try and get enough distance to ‘mute’ any future attempts to dominate their wills to any future Lich Kings, and the secrets of raising the specific types of ‘High’ Undead such as Death Knights, San’layn, Liches and Frost Wyrms was either lost or became known only by a handful of individuals.
The Death Knights we raised during Legion, and again at the end of the Battle for Azeroth, were only possible because Bolvar had made a pact with the Death Knights of Archerus and was willing to raise willing souls into the eternal service of protecting Azeroth from all possible threats. Lichdom is possible even for individual Mages, Sorcerers and Wizards, but even then, the process has a hideous mortality rate if you are not trained in the ‘correct’ method of binding the spellcaster’s soul to their phylactery, and Frost Wyrms are shockingly rare to find and exceedingly powerful even when raised from young and ‘teenage’ Dragons.
