Our current idea is to connect different levels to each other through specific "gates" where we can stream out the level you were just in and stream in the level you're going to. In those gates, there is gameplay, it's just not so diverse as a level is.
Can you 'stream' back to a previously visited level?
On the topic - Oblivion/NWN/Baldur's Gate load in the interior of houses as different levels. Gothic doesn't. Both methods have advantages and disadvantages - which do you prefer ?
If it is fast enough to load, it hardly matters.