Why not attackable, like any other existing surface building? I think you probably meant "destructible", and there I would dare to state a clear no - again like any other surface building. Persistence should be no issue, it's just a few coordinates being stored on the central server. At least as long as these buildings are as uniformly like the current existing ones with no individual design. If that really will be that exciting remains to be seen.There are plenty of permanent structures in elite which have no issues. P2P should not be an issue as I suspect it will all be kept server side if it does come like the rest of the galaxy is.
I also doubt bases will be attackable. They will likely have lethal defences like stations with a proximity warnings to stop landing bay hogging.