You're a genius! I've been trying to diagnose what was causing the remaining rotation bug, but I haven't been able to replicate it reliably until now. I'll get a patch for that out soon!
I largely agree with you about the soft and hard drops, though only awarding points is a direct carry over from Tetris. Bonus incentives on the board for fast play is a good idea... I'll have to think on how something like that could be implemented. I'm open to ideas!
The game doesn't actually speed up as you play, though that is on my list of potential features! My only worry is that, once you get to mid-to-late-game Tetris speeds, everything will be moving way too fast to reasonably keep up. Maybe that would be best suited for an optional challenge mode.