Honestly, if I was the lead dev for “Classic+” Classic actually wouldn’t be the start point.
So the 8 starting races, and the 8 classes per faction get to be the first casualty. But then, that’s part of why I’m a bigger fan of the “Walled Garden” idea and Classic+ seeing implementation through retail(and ostensibly the Bronze Dragonflight). We bring anything we want from the future back to “the Classic Era” while trying to maintain as much of Classic’s core gameplay as possible.
This means Shaman is playable for Alliance, and Paladin is playable for the Horde in Classic+.
While Bagspace management was a memorable aspect of Vanilla, and should be replicated in Classic. I don’t see a reason for it to persist in a Classic+ iteration. This means Guild Banks would be viable options, as would be the collection tabs, as initially implemented in Wrath. That means per character, not per account.
The BattlePet system is a little weird in my book, but I don’t see any particular reason to kill it with fire either. It could be brought across, or left behind, I honestly don’t care. As a mini-game within the game, it has its merits. Don’t like it? Play Classic, not Classic+.
It also means I’m able to pick and choose on some other items. Stormwind Harbor would likely be present in Classic+ from the start, as initially implemented in Wrath, complete with the undestroyed Park District.
Stormwind Keep would get an upgrade to its current form, complete with accompanying park that was used as a nexus for Cataclysm and MoP. Orgrimmar would likely see selective upgrades to it as well. If you want to see them in their original form, play Classic not Classic+.
The Classic Game mechanics are in full force, Classic Talent trees are the starting point. Any additional classes/races brought into the mix will have their trees adjusted to conform to the game mechanics paradigm of Classic(+). Talent tress will however, not be static, so re-balancing can, and probably will, happen. But every effort will be made to keep it within the bounds that the devs demonstrated up through patch 2.0 as it basically is a “bridge” between Vanilla and what TBC ultimately became in 2.4, because honestly, 1.12 is basically 2.0’s talent trees scaled to level 60 anyway.
I would likely allow many of the additional Flightpoints added to the old world in 2.x(not Cataclysm) to be brought into Classic+ that said, you’re still waiting for level 40 to get your first mount.
Phasing would get an overhaul, with some rules tweaked along the way. In many respects, it becomes war mode meets layering. Because yes, I would be using the ever-living daylights out of phasing, but only after some of its more annoying quirks(Especially for PvP) get sorted out.
Group content is going to be retuned as well because of these changes as well.
No (player controlled) flight in Azeroth.
LFG might be allowed on a per realm basis, or collection of realms in the event of low populations. But no LFG selection pools numbering in the tens of thousands.
The list would keep growing from there as other systems are considered and evaluated.