That's a fascinating question! As the owner of a Boosted Board and a scooter, I always go for the board because it's 10x the fun. You can shred on a board but not on a scooter. You can pick it up and bring it inside with you for meetings.
Sometimes when friends come over, they want to try out the board and their faces just light up:
I'm skeptical that they could get widespread adoption on a rental because people without skateboard skillz are afraid to hop on and think they're dangerous. They have a separate controller. There would be more injury and loss and theft.
Too bad because they are so. Much. Fun!