I'll just mirror concern on crystals to 99. For a lot of mobs, that'd mean having to kill 99 non-elemental critters solo to make yourself a stack, and mobs don't always drop a crystals (sometimes they just plain can't, be you in Abyssea or in a Beastmen held zone). Without an actual overhaul in available AH space, people will be limited to selling 1 at a time in a lot of cases. From the buyer's end, I don't want have to sit down buy 20+ individual crystals if the options are just 1 and 99. Retaining the 12 would also mean the AH would need to institute another check in the listing process to not only remove the listed items from your inventory, but to guarantee leftovers aren't eaten. That might introduce some complications into the item ID process, especially if you have more than one stack.

Seriously. 12 > Cluster option > Stack Clusters to 12. Even when Colibri were the in thing, I don't think I ever walked away from a party with over 144 wind crystals, and it wasn't for lack of space in that level range.