What do commercially produced electric motorcycles use, and can any of that be salvaged and adapted?
DIY connections to EVSEs are pretty pricey and bulky.
Best to also allow slower charging from stock 10A 110Vac as well as 240Vac outlets used for driers and electric stoves/ovens in the US.
Charging amps to get faster than say a 90-120min charge will shorten lifespan.
Charging through a J1772 connection to an EVSE can be just as slow as plugging directly into an uncontrolled 120 V or 240 V AC outlet. The EVSE only adds safe and convenient management features, not higher charging rate compared to directly plugging into whatever circuit the EVSE is connected to.
The cost and bulk of the onboard equipment to work with common EVSE is certainly a concern, but it would make many more public charging locations available; at home it would be unnecessary, but the intended use is obviously public locations.
Due to the combination of low charging rate and the tendency for charging stations to charge by time (rather than by energy), unless you're using "free" (complimentary, provided by retailers or governments) charging stations this can be an expensive (in terms of cost per kWh) way to charge, but a motorcycle uses so little energy that this might not matter. For example, the only paid public charging station in my area charges $2/hour for AC charging at up to 7.2 kW, which at $0.28/kWh is three times the value of electricity here, and $1.42/kWh if only using 1.4 kW (a typical 120 V onboard charger) which is ridiculous... but still only a few dollars to charge the bike, and $4 for a full charge if following the (reasonable, I think) advice to target a 2-hour charge.