Awesome idea for a homebrew! Never understood why the "Sega mascot" didn't get a Sega pin, especially with Spinball being a really fun Genesis game and the theme overall lending itself very well to pinball.
That mystery scoop should have the little computer monitor over it with a micro LCD inside and either give you 10 rings, invincibility (unlimited ball save), fast shoes (scoring), Tails (2-ball MB), or spikey ball (loss of rings). I assume 100 rings gets you Extra Ball?
And I don't know how it could happen, but with what looks like a spinner in the right ramp, if it could be a horizontal spinner that flipped images between Sonic and Robotnic, but always landed on Sonic (emulating the end of a level) that would be bad ass.