Realistic planet size like Infinity or Outerra?

Outerra and infinity are realistically scaled, and KSP has the tech required for Earth-size planets - once you get the basic tech for allowing big planets (LOD scaling, floating origin / high precision numbers, procedural generation for more detail than can be shown in a relatively low-res heightmap, and some more), you can generally start scaling the planets up infinitely provided you have enough memory.

Also KSP's Kerbin is 1/11th of Earth's size, not 1/100th.

I know KSP is capable of doing it, however at these scales you are forced to use procedural generation for everything (apart from the height map), as you would need a very sophisticated system to compress any customizations and still don't overflow the server with data, along with what bgolus said.

To prove that I know what I'm talking about (and to plug my project of course )
This is a procedurally pre-generated, fully custom planet, consisting of 4.7 gigs of data for a planetary radius of 10,000 meters (~1/600th earth scale). This is probably something you do not want for a multiplayer game:
http://www.youtube.com/watch?v=jj1Gc5buoEw

As for Kerbin, I didn't look correctly, my bad

Anyone like the idea of loading up parts of google earth into PA? It would be awesome if you could translate the 3d models into PA and have it destructible.

The short answer is no. As Ben said we need to have the entire planet around for things like pathfinding. Realistic scale has never been and won't be a goal of this project as it's just simply makes no sense for this game.

Even things like asteroid orbits have to be insanely different than real life. Otherwise you would be waiting for a few years to get any impacts. Real life scale and rts games simply don't match up unless you are doing something extremely small scale.

If our goal was to simply make pretty planets to fly around we would take a completely different engine approach that was appropriate to that goal. As you guys have seen other people are actively tackling these types of problems.

I think the planets need to have play areas not too vast, I like big areas, but I don't want to transport for 25 minutes to get to the front line either.

However, who said the planets need to be spherical - before you laugh - I was thinking how about adding orbitals - as in Iain M Banks novels, or Halo. Not to that scale of course, but inline with area of the typical PA planet.

This might make for some more interesting strategies, and gels nicely witty the metal planets we expect to have.

Unit canon to the opposite 'wall', rocket bombardment from above, no fog of war, as there is no horizon anymore. So, lots or planet based strategies and tactics go out the window!

Slim

Neutrino has said that this will not be in the initial release, but that it might happen in the future.

What about a game on a single -but big- planet map with only orbital neighborhood ?
The planet don't need to be 1/1 Earth sized, but big enough to completely dwarf current biggest supcom maps (needed for 40 players on the same planet) and to smooth enough the curve (less disturbing distorsion that bring too much cartoon looking IMHO).

Travel time and empty space won't be a problem since we can have very fast air transports, teleporters, very efficient scanning and targetting satelites and radars as well as efficient UI order system and autonomous enough AI.