I’ve been playing very little week after week and I have been accumulating these crests. I am sitting at 28 whleping crests but with a couple of lucky LFR drops I can’t really upgrade anything.
Will we be able to pass these to alts in the next patch? Or anything?
in 10.2
UPGRADE SYSTEM
Hero upgrade track length increased to 6 (was 5).
Myth upgrade track length increased to 4 (was 3).
Crests are now currencies and will no longer take up inventory space.
Fragments have been removed. Sources that previously awarded fragments will now award crests.
Once a player has purchased all possible upgrades with a type of crest, they can visit Vaskarn in Amirdrassil to exchange those crests for higher level crests.
For example: Using Season 2 item level numbers, players would become eligible to trade their Whelpling Crests up to Drake Crests when every gear slot had reached item level 411 or higher. Trading up to Wyrm Crests would become available at 424 (again, in every gear slot, using the same rules as crest redundancy), and trading up to Aspect Crests would open at 437.
No they will be gray vendor items on Tuesday.
Likely no. In the past, old crests are useless in the next patch. Last time (10.0 to 10.1) I think they offered us a conversion of old crests to gold at an NPC near the crafting order station in Valdrakken.
vendor them maybe?
Create a whelpling with them. 
Actually it would have been good to make a whelpling pet with them or many with different color variants.