I think they did say they were not planning on doing mounts for each class, but doesn't mean they wont eventually or that it isn't a fun topic to discuss.

Archer - or maybe a Bandersnatch (like from 7 not 9.....)
Conjurer - Uni
Lancer - Drake/Wyvern/Duh.
Arcanist - Should have carbuncle slippers. Just saying.
Marauder - Adamantoise Would fit the tank thing or Behemoth why not?
Gladiator - Some type of Griffon/Manticore would be sweet! to tie in to FF ?!Griever?!
Pugilist - Tiger....that's all I got.....
Thaumaturge - Cockatrice? maybe too close to a chocobo