Man that sucks. they make good games too in my opinion, this one woulda been cool.
I've asked for opensource in discord and no response(probably they will not open it just because there a lot of work done and maybe they will return to it in future).
I've modified a bit Alfa 0.9 version(more enemy for each wave (x2, x3, x4), more time between waves to build more defense and economy, possibly will add some more features like longer storms, more or even endless waves ), I did it just because wanna play more in this game) So if someone wanna - I can share it.