I imagine this would be super-simple, because the Starmade engine uses different entities with their own grids, in an overall universe. The "tardis-verse" would simply be an oversized entity, where the Tardis blocks would represent the entry/exit point.
However, I don't think this will be accepted as a feature of Starmade. Reasons:
1. The Schine team has repeated over and over that they don't want different "universes". They want everything accessible in the same universe. This would include Tardis/Bag-of-Holding micro-universes. The only exception is cargo, and currently, the ship's core (see point 4).
2. Beyond deactivating/prohibiting any system/weapon/power blocks from the Tardis-verse, there is no way to make this adequately balanced in the game, even with massive power requirements. And in terms of system blocks, I can't imagine the playerbase being satisfied with a non-system, all-decoration "Tardis-verse".
3. When the Tardis blocks are destroyed, how much of the "Tardis-verse" is ejected as a loot cloud? Sure, you can eject a single player from the block, but what if there's a whole bunch of people in the Tardis-verse? Half the community will insist on mutual gibbing of all astronauts if there's more than one, and everyone else will insist on an unworkable multi-astronaut ejection.
4. In effect, all ships currently have one, and exactly one Tardis-verse: the 1-m^3 core, into which the pilot slips during ship control.
