I too have found myself wondering what a strap-on session would be like, and the fantasy is not so much about the strap-on itself as about the muscle-woman wielding it and the thought my defeat at her hands could be that complete.
I realise it's not something I'd want to go through with though, partly because of the physical danger but what I think would be really hot and would closely match the humiliation, is if a woman rode me from behind with just her own natural (if somewhat enlarged!) equipment, slapping and grinding herself furiously against my buttocks until she came. A woman who was a lot more powerful than me and well able to hold me in position, and whose thrusts rocked my entire body.
I'm a bit surprised it's not a scenario I've seen played out in videos and reviews.