I like the lines of the bike, also!
And, I would like to see someone mount a chinagirl up on top of that step-thru frame!
It could be done.
It would not be as strong, or safe from cracking as a top-bar frame, though.
IMO that would be less an evil than relying upon a sole coaster brake for stopping a motorized bicycle.
A string trimmer rack mount friction drive would be the most logical choice for your cruiser bike.
Or a hongdu solex.
NOT a overwhelming majority of solex fans here! lol
I'd like to try one, someday...
Best
rc