I'm still leaning Mosaic core with a different interface board (or different firmware on it).
The Nano is 25fps, and the best I can tell, has a shutter.
The Micro core is only <9fps, and shutterless.
The Mosaic core has an "up to 32fps" variant, and has a shutter.
External dimensions of the Nano are 25x25x22 mm. Mosaic core is 20x21x10mm to 21x23x20mm (depending on lens), so would just fit inside the case (with room for an interface board behind the less deep lenses).
Guess we have to wait for someone to get one and tear it down.