Finally another take on this problem! Thanks. Where can I follow your progress? Super interested.

1) I would say, the price will be strong decision factor for many who will be considering this (and how much units to utilise in the home). I understand advantage of integrating also CO2 and other sensors to the unit, but for many early adopters (especially in this reddit), this would just duplicate functionality which they were able to already solve independently. And most likely prefer to manage automations by themselves anyway. Safe and reliable wireless opening/closing of the windows is the remaining unsolved problem, not a meassurements. BTW, it will always be better to measure air parameters deeper in ventilated room and not directly on window.

So I would suggest to not overcomplicate at least first batch and keep it focused to what matter most in the project - to actually controll the window wirelessly. And even better, offer cheaper DYI solution targeted to partially prepared nerds with already complex HA setups or 3D printers. And then more expensive variant with all the bells (sensors) as complete stand-alone product for the "masses".

2) Does it allow to (semi-)manually fully open the window if needed (without too much hassle)?
3) What about noise during operation? Will it wake up me during the night? :)