If you ever find yourself in a fight with this guy, just but scoot. All the kicks will go over your head, and sooner or later you may be able to hit x-guard or something.
Someday, someone in MMA will land a jumping, sideways, spinning kick for a KO. Give it about 10-15 years. Till then, anyone who tries one in MMA will probably just get kicked while "flying" or get taken down.
I enjoy watching the gymnastic aspect of the kicks. There is always that element of surprise that might catch someone. Useless probably, looks awesome, heck yeah!