Runescape Legacy Mode
Really, just move coin pouch to the equipment screen along with the Wardrobe. use the space from the bottom of the inventory and add another space for "bars", fuse the magic, melee and ranged tabs back into their pre-RS3 interfaces, the combat button on combat bar should bring up a small menu showing combat style/xp tuning.
Throw away the ingame highscore/events tracker. stick friend/clan/visiting clan chats into a single button. have a toggle to swap easily. seriously. at the moment you can't even check your clan's list unless you happened to have it.....crammed behind 6 or so other tabs. all because you might want Magic, melees, HP, Inventory and Equipment.
Or maybe you can add a system that enables players to create their own hoverbuttons, and "inventory screen" bar placements, convert them into code and post them on fansites or the mainsite for people to rate. to keep bandwidth down, it could have them generate on the viewers end, with the only assets being loaded are images saved on the site.All in all, i miss the old stones-style menu system. it was much more simpler to navigate without all the bells and whistles of stuff such as runescape gold.
EDIT: Also, graphics or at least the text should be vectorized, so people could resize those for more customizability, could free up a bit more space, maybe even more so if graphics were vectorized.