This was a lot of fun to make! I think the large scale form is A-A', where A' is more intense. It somewhat drifts in feeling, but I hope it adds up to a coherent whole.
Maybe it has a little too constant thickness of texture. It would be nice if there were sections with more breathing room, but it's as if the piece rejected my attempts at such transitions.
It's a first time for me mixing ensemble strings with solo strings. I hope it's convincing. There are some harmonics glissandos in the solo viola and the solo violin. The solo violin even plays tremolo harmonics in the background at one point.
I tried to make sure the viola's harmonics melody starting at 1:28 and 3:46 was not too fast, because I imagine it must be almost as difficult as double stops. I also imagined that it's best to use slow-ish gliding between harmonics notes, since more fingers are involved than usual, so I imagine it would be hard to change notes abruptly. Please correct me if my orchestral intuitions are wrong. It happens :)