I haven't researched this, but I was told by a neuroscientist/martial arts-practicing friend that particular sports (like martial arts) where you have to practice a very wide and varied range of technical motions and thus challenge/develop neuromuscular systems widely may be particularly good for general brain health and plasticity (in the same way that varying your routine widely, etc, apparently is). Seems plausible, but I repeat that I haven't researched it.
Big wodge of evidence about karate in particular (not martial arts in general) being unhealthy.
A lot of it is about karate masters-- it's quite possible that if you stop when karate starts seeming like it's bad for you, it's not all that destructive.
I've poked around a little to see whether belly-dancing and tap-dancing (complex movement of very different kinds) increase longevity, but haven't turned up anything.
This post is a bit of an experiment; Most of the time, Discussion post lay out an idea and this idea then get commented upon. This post, on the other hand, will be purely about discussion on a topic. If this works out well, I'll might post more of these in the future.
On to the meat of this post:
I got this idea from a reddit post on /r/LessWrong.
To quote:
So have at it.
I only ask for one thing and that is to hold off on proposing solutions for 24 hours before giving suggestions for actual sports. In the first 24 hours, please discuss what makes current sports unappealing to rationalists and what aspects a sports designed for aspiring rationalists should have.
Edit: The 24-hour window has closed and solutions and suggestions can now be given.