Oh wow! That's cool. I did see this post a few days ago and I have been thinking how I can increase difficulty each time it loops. Unfortunately increasing the speed of the enemies is not that straight forward because of all the fixed point maths. I'd probably have to create new enemy data for that also.
Alternatively making new wave data for arena 2 and 3 is probably the easiest option but would require a lot of playtesting if I'm changing the waves and enemy counts.
The original plan was to add another 18 levels with new enemies and patterns, 2 new bosses, and possibly some other gameplay modes. But I have too many projects I'm working on and my attention has been elsewhere after the AGA version.