Daft as it seems, Canon could have got away with using the E12 battery by offering the option of an external battery pack using a USB power brick with a USB cable or a battery replacement unit in the style of the mains units available for many DSLRs but connecting to a power brick with belt hook for quick release.
Sounds a bit far fetched?
Well it is available....
Ex-Pro[emoji768] Canon DR-E12 LP-E12 On-The-Move 16000mAh Rechargeable Battery Power System replacing Battery Grip Battery for Canon EOS M, EOS M10
https://www.amazon.co.uk/dp/B01M5KQQSY/ref=cm_sw_r_cp_api_XYFLAbZPWKBF3
If Canon were to build this into their offering and properly support it then it could be rolled out for other models. Naturally it might hit margins from extra/replacement batteries....
All day shooting anyone?