I'll double-check the window size storage, and I'll look at adding mouse support.
I'll have a think about adding some of the extra non-ST features, but I really want to keep it ST-authentic as that's the version I'm most familiar with.
And no, the ZX Next has limited resolution so I wouldn't be able to use the higher res graphics in any case.
And no chance of a Mega65 version - I don't know that any programming for that machine at all. However, I'll probably be releasing the source code at some point, so hopefully someone can do that.