I would love it if we were able to share plat between characters without having to go thru the mail system or finding a third party to play the trade game with.
Put a plat line in the shared bank account just like you have on your character sheet, one without a 4 digit limitation. This would allow for the transfer of larger amounts of plat between toons. By doing this, it eliminates the need to send multiple 9,999 pp posts to your other toons when you are ready to re-gear them.
I know its easy enough to have the toon with the pp buy the items then drop them in the sba, but when you have multiple toons, it can be difficult to keep track of the gear/weapons your alts can and cant use. It would make life that much easier.