http://www.mongoose.com/usa/fireball-350

Almost precisely what I was looking for my next attempt.

Aluminum frame on a 20 inch bike, should be light.

V-brakes back and front. Good stopping power.

One piece front fork. If it had shocks, they would bottom out. Ideally, it
might have some suspension, but I have an exceptionally springy and
comfortable aftermarket cruiser saddle (Serfas FS-CR).

Rear derailer with sprockets up to 28 teeth. Probably can be upgraded to
34 teeth if necessary.

Apparently the chain is 3/32 inch and the bottom bracket is a standard
bicycle square taper type (the latter being a big bonus over a BMX bike,
for my purpose).

Thirty-six spokes for decent strength. Many have only 32. Ideally could be
double walled rims, I guess.

Ideally, the tires would be street tires but at least they aren't full out
knobby.

Besides not having suspension (that would make it more complex/expensive),
not having street tires is the only real drawback. But of course tires
eventually get replaced.

The fact that it's small with 20 inch wheels isn't such a big deal since I
won't be peddling. Most electric scooters have smaller wheels than that.