If there's a way to generate a simple digital click guide (selectable option in menu) while recording, that would be optimal to have... but not required. It would just be dependent on being slave to a drum machine or other master source... but that would be fine. I'm guessing that, like me, many others have their Pro3 permanently slaved to a drum machine, DAW or other clock source anyways.
A couple thoughts on potential implementation:
1. Consider using the Footswitch Pedal Input (or Sustain input) as the "Recoding Activator" for Real Time Recording, when the Realtime Mode is Selected in menu and the sequencer clock is running.
2. Have two recording arm modes (selectable in menu option, or maybe a shortcut with Record button and something to easily switch between the two):
a. Continuous Overdub Mode: As long as the Footswitch is held down, it will continuously Overdub notes, looping around and around for the entire sequence length... each pass could potentially add new notes to the sequence.
b. Punch-In Mode: In this mode, the Footswitch pedal would perform a "punch in" recording mode (ie: Erases/Overwrites whatever notes are currently in the sequence, and replace them with any new notes played in real time. If you held down the footswitch in punch mode, and didn't play anything, it would erase that section... you could, on the fly, press down on foot pedal, and replace the whole sequence live over a measure and then release the punch mode and it would just play the new verse you recorded.
Having both overdub and punch-in modes would be useful in this type of monosynth context... allowing build up of a repeating sequence, and ability to switch up the verse on the fly.
To me, there are many other Feature Requests in this thread that I would prioritize over realtime recording though (more mod destinations, glide in sequencer, probability in seq, more arp patterns, paraphonic note priority modes, etc) ... assuming its going to be a significant project to undertake. For looping with the Pro3 (and other synths), I usually just use a dedicated Looper Unit (like the BOSS RC series units I'm currently using, or a MIDI recording sequencer like MC-707, MPC or Elektron unit) But, yeah, would be cool to have realtime recording as an option.