Chains are very efficient (non o-ring ones), and very strong chains are available (similar differential to the one at the link was used on a racecar running 230hp through a chain), but adjustment could be an issue.
I wonder, in an automotive setting, if it would be practical to have the chain run inside a housing so it could be continuously lubricated and kept clean. Timing chains seem to last practically forever, for instance. They have nice continuous tensioners, too (oily chain slides on long curved spring-loaded poly blocks).
Interesting issue. Size/shape of the space available might be the determining factor.
And then there's belt drive...
__________________
|