Rollerblading sounds like fun, but as for me, I've got a lousy sense of balance.
I don't think your ideas are crazy at all, although I am of the "Why would anyone jump out of a perfectly good airplane?" school of thought. (I also frequently ask GBMD why anyone would sink a perfectly good boat, but that's a different subject.)
If you want to do it, why not? I understand the fear of injuring your knee further, though. (Speaking as someone with bad knees herself.) Perhaps talk it over with a doctor specializing in sports medicine?
Me...I want to learn how to dance. I keep learning, and then forgetting.
I can remember how to cumbia, but that's about it. One of these days, though, I'll learn
and remember!