I think having a throttle on a gear shifter might me a good idea for a motorized bike because we don't have a lot of pull anyways, here is an example I can think of to FULLY integrate the standard shimano tourney gears to a motor. I have already modded a bike to run the choke off the unused left gear setup as shown (i had to solder down in the brass fitting) I suspect that with 7 gear "options" available on the right, you could also remove the standard throttle and just "shift up" in order to "add throttle" a cruise control as mentioned.
Of course it does not get by me that it is possible for the bike to continue running after someone falls off for whatever reason but if going down this route I would further integrate a "kill swith" not unlike on a sea-doo (jet-ski) in order to make the bike die upon falling off. The sea-doo kill switch could also function as a safety (key for ignition) so no-one could just hop on your bike and ride off. Because the wrist band sea-doo kill switch mechanism would function like a "key."
The conbcept for a kill switch could be routed before the CDI and after the magneto.