@Ziqal Personally I'm ok with no gate outputs anywhere. It's up to the user to mult the MIDI (this sometimes works with a TRS split cable) via an external device or even using a few of the available MIDI mult modules available. That would allow the user to plug to a MIDI-to-CV module and use the gates from there. Additionally, some MIDI-to-CV modules (I'm thinking of Flame) have MIDI Thru, so that would also work just fine. So, for me, SYNC input as TRS MIDI Input would suffice.
That being said, if you allow for a 2hp expander as you suggest, would the MIDI connection happen via pins the back? That would be ideal, as that would allow for modules that have their MIDI outputs as pins in the back to connect directly to the ZIQAL with no cables, which is always nice.
Finally, if you want to avoid redesigning the PCB to add expanders, I can suggest a simple workaround. Use SYNC for MIDI IN, and set an option so that one of the L/R outputs sends a gate when incoming MIDI messages are received. That would be an option for the user that doesn't have a way to get gates otherwise (although I do believe that's up to the user to handle, this is an oscillator you're offering, it's not your responsibility to handle the MIDI-to-gate, in my opinion)
PP.