um, the Doctor could scroll though some different console rooms before making his decision, or it could be the console room of another TARDIS, however asking viewers to design a console room for the TARDIS of a timelord we dont know, would be kinda tricky.
truth be told im not keen on this kind of thing, we pay the BBC to make our TV shows, not to ask us to do it for them, Doctor Who has plenty of examples of this
1) the alien from Love & Monsters was designed for a Blue Peter competition
2) the alien featured in the "mini episode" on Tonight's the Night was a fan creation
3) the Doctor Who Adventures magazine ran a competition to design a companion for the Doctor, to feature in its comic strips
4) some kids from Totally Doctor Who featured on Doctor Who at some point (not sure when)
that is before we even consider the awful "A Fix with the Sontarans"