Beta access as IAP?
Or, since Apple is probably against that, maybe a "Tip" IAP that gets you beta access? That would be awesome, even if it's not as a full beta tester, but just grants access to early releases and read access to the beta board.
There are several upcoming features that I'm nail-biting anticipating, like MIDI mapping of the step sequencer buttons, and USB control surfaces, among other roadmap features. (if it helps, I've got a ton of various MIDI controllers 😉 ). I'm still fighting the urge to get a Digitakt (and ending up with a Digitone, too...)
I'm also all for financial support that makes ongoing development of Drambo sustainable, as I see it as a reason to buy a dedicated iPad, especially once there's tighter hardware controller integration