Idea: Space.

A dimension available by flying above Y:300 in a TARDIS. It allows you to see all available planets/moons/anything but Nether, End and TimeZones. Flying onto the surface of one of these will act as if you flew there via the monitor. 

The most recent time zone varient of planets wil be shown (eg leave CaveGame, the planet Minecraftia looks like CaveGame. Leave snowy Trenzalore, Trenzalore has snow instead of the black texture).

Maybe all of the TARDIS' are visible in space.

Also, have the monitor changed so you select the planet, then the time zone with different buttons. Just an uncluttering thing.

(Posted on MCF and SWDForums)

That'll take alot of code.

 it would but think about it, it can just be another planet on the tardis monitor with 0 gravity and the ability to use the flight panel

 I've already suggested the thing about the Monitor (Time zones would be selected via up and down arrows in the gui while left and right arrows select planets)

As for space, yeah, that'd take a LOT to code. I mean they could do something like galacticraft, but it would take a lot of code, and flying from planet to planet via "space flight" would honestly take too long.

The tardis isn't really the fastest vehicle when it comes to non-vortex space flight.

Additionaly, it is canon that the Tardis was not designed for extended periods of space travel outside the vortex (it begins taking damage after a while). This happened in one of the Pre-Rose stories.