Normally the engine is already able to have large maps, and streaming is mostly used to reduce strain on the client, so they don’t need to run everything at once.
While people’ve been throwing around “just level stream in source 2” I’ve not personally seen much to do with source 2 actually doing level streaming. The closest one I can think of is the ‘recent’ dota 2 event which had a semi-random dungeon crawler experience. IIRC it used some map stacking method and actually still stayed inside the source 2 map bounds.
If you wanted to do level streaming within the bounds of the current source 2 limitations, I think you’ll have to be passing players around servers that control a different map, with some connection handling to make it transition well.
in the context of spacebuild / starwars RP, you’ll have to hide the servers behind some kind of ‘warp drive’ or something similar. Another possibillity would be to share the map edges with other servers, but people’ll probably be able to notice when suddenly an entire map worth of players pop in.
Realistically, I think we might get actual level streaming after they expand the current map limits, we are able to load maps inside maps already.