Very cool, and definitely fills a need. I think I'm gonna try this on my Vita through an old PSP GBA emulator.
And thank you for actually using the full real estate of the screen for gameplay! I'll never forget going from Tetris DS to Tetris Party Deluxe on NDS and immediately noticing the smaller blocks, all because of some dumb border at the bottom that just shrunk everything else.
If you're taking requests, how about a 4-wide combo race like Nullpomino has? Official games don't have that.