I think it would be really cool to have support for a "backpack" of sorts. Your first 5 equipment go into your inventory like normal, then any other equipment you get goes into a hidden inventory that you can access by typing /backpack. /backpack opens a GUI that allows you to see your 5 active items and then 15 additional items. While in the inventory, you could change which items you hold (similar to how the brick inventory works).
There should also be a trade option to go along with this that'll allow you to type /trade username to trade with that player. The trade menu would act like the backpack, but there would be another section for what you want to trade and what they want to trade.
Of course this mod would have to be done on the server side, but there should also be clientside keybinds. For the trade one, pressing the bound key would make a gui pop up which you can type the user name into.
I'll try to post concept picks in a bit.
