That seems like the best option. Adding a motor to a longboard is just enhancing a known proven quantity. It won't have the maneuverability of a onewheel or the all-terrain ability, but longboards are definitely a proven vehicle for roadways so motorized ones seem fine.

Maybe there's some variation of the kickscooter that can meet the portability and compactness of a onewheel. Something that focuses on the foldability of the old Razor scooters. But that still wouldn't be as convenient.

Fundamentally, the onewheel seems like a personal-mobility answer to the V22 Osprey: a vehicle with amazing functionality and versatility in its happy path, but is fundamentally unsafe in failure because of the basic physics of the situation.

edit: onewheel, not longboard, in the final paragraph.