The coding for the new system would be insane. This idea has been submitted to Jagex on numerous occasions. I still support it because the current banking system sucks!
The current bank stinks. You can never find anything on f2p much lesss in a members bank with 100's of different items in it. It woould make it so much more organized to have this bank. I cant see how they couldnt make it f2p. I would imagine the coding for the bank is applied to f2p and p2p