Very stable. They could ship it like this IMO.How stable is it for a beta?
There is no geometrical size limitation AFAIK. The limit is given by your thermos, so there is a finite number of objects, logic and music but you can zoom in any stuff as big as you want. And cloning and enlarging objects doesn't cost much.1) How big a level can you create? Some have voiced concerns that the engine can't cope with large levels full of geometry. 2) How far can the physics go? Can you set up an avalanche with loads of objects? Can you shatter objects procedurally?
I have seen levels with as much details as many recent games and with tons of animations applied on everything. I'd say a dream with as much details and animations as TLOU on most scenes (excluding textures details where things would have to be simplified) is possible on Dreams if you are smart with the way you deal with the thermos. There are plenty of new tricks and progress to be made. We are not dealing with polygons anymore.
About physics there are already games with physics applied to the grass when you walk on it. I have seen 2 different implementations of physics on grass. Very very convincing stuff. But I haven't seen much dreams yet.