Suggestion: I think it's be nice if every TARDIS had a small side room with a small set to starter tools, such as a furnace, crafting table, a couple of chests, and a bed (oh yeah, please make them not blow up).

How it benefits: Well it makes the TARDIS more neat and tidy. I know you want us to do our own expanding, but a side room would look nice, and you could a door in that room to start way for building custom doors. Also usually people just build chests and furnaces all around the console room, which is messy. 

How it'd look cool: Make each side room in style of the TARDIS interior, so it looks consistant. Also you could possibly add previously seen side rooms, like the Drawing Room from the Adventure Game: TARDIS, or the number of bedrooms and shit seen in the classic series.

Side note: if this isn't added then i'll drop a nuclear warhead over London.