>> The Solvespace UI is a long, long way from being the sort of UI a contemporary kid has any kind of comfort with...
Respectfully, I disagree. Even adults have used the word "fun" to describe using solvespace. But I don't actually have feedback from kids, hence the question to OP.
Don't get me wrong, I think Solvespace is really important and I am glad you are keeping it ticking over, but it is the least fun UI I have ever encountered, I'm afraid (kind of obtuse on a trackpad too)
Not saying any of this is easy — Shapr3D on an iPad, expensive and marketed on its extraordinary usability, is just utterly perplexing!