I think they would simply just adapt the TARDIS. As previously said, the Doctor Who Experience walkthrough with the TARDIS’s arrival and you step into the box to find yourself in a room that’s bigger on the inside is probably our biggest clue at how a Doctor Who Land at Universal Studios Great Britain would work.
Maybe you’d then have a ride inside that takes you through a few of the TARDIS rooms, with animatronics of past companions, or something involving enemies of the Doctor’s, like the Daleks or the Cybermen.