Chinese electric bikes are the next frontier, and still elusive every time i check. Sourcing integrated motors & batteries is a problem, there's usually high MOQ. Obviously sourcing suitables frames isn't easy either, but it's easier than sourcing the right motor kit. It gets expensive, too, so for something with a lot of unknowns, it's quite a commitment. For what i need the bikes to do, i also need a jail broken software because an electric bike maxxed out at 25kmh is entirely useless, and that is also a problem. I'd build road bikes for girlfriends and slower guys to ride up to at least 40kmh, so we dont drop people.
The only practical route i know of that involves not buying something off the shelf is a bafang kit on an aluminium frame (you risk crushing the BB area if it's carbon). JohnnyNerdOut is a great resource on youtube.