More people would try playing an instrument if they could borrow one to try it out. I already play several, but I’m running out of money and space for more. It’d also be nice to pop down to the library and check out the one I’m currently obsessing over to see if I want one permanently. Hell, I’d donate ones I hardly ever use to add to the diversity. This wouldn’t replace buying instruments any more than regular libraries ended book stores.
Do you mean “can play a musical instrument” as in “knows how to” or “has the potential to”? Obviously not everyone knows how, especially if they don’t own one. But I think basically anyone has the potential. Screwing around with an instrument helps you figure out if if it’s a halfway decent fit, and with the Internet it’s pretty easy to learn enough of the basics to figure out if it’s right for you.