In the meantime I've had a think on the possible ways they might implement spacelegs. These are the ones I came up with.
1. the most likely way I think is that Spacelegs will be implemented is practically the same way as SRV's are at the moment. As in you select once landed on a planet/planetary base how you want to exit the ship. If you choose legs the standing up and fade to black animation used for SRV's plays and you get 'spawned' near the exit of your ship (i.e. near the backdoor on a sidey or at the front landing gear of the python etc.). Hopefully you'll be able to change your loadout upon exiting your ship, instead of having to choose one on a station as with your ship.
2. You'll be able to actually stand up from your pilotseat once landed at a station/planet and you'll be able to walk around the cockpit. To get out you'll have to walk to the door at the back of the cockpit, you'll get a fade to black and you'll appear outside of your ship near the most likely exit as stated above.
3. Depending on the size of the ship, their might be some crewspace on the ship, that you'll be able to walk around and to get out there'll be an exit somewhere you need to take.
4. your ship's interior is fully implemented, including all modules and you'll be able to walk around/in them. And the exit is through an airlock where you'll either get a fade to black or a seemless transition to the of outside your ship.
I don't think you'll be able to get out of your seat while the ship is flying, either in normal, supercruise or hyperspace. Due to the fact you'd have to get back to your seat to pilot the ship.
I think 1 and/or 2 are the most likely way they'll implement the transition from ship to legs. And that we're hoping for 3 and/or 4.
Let's hope they'll give some more information soon!