There's a number of hiccups but nothing that strikes me as impossible to manage. You and your karma rich folks could "invest" in other posts as much as you'd like, but if the non-Karma rich don't offer a simple upvote, I don't see why you'd receive a return on your investment.

There'd also need to be some element of time, so the sooner you invested the more you can potentially make back. And perhaps if you invested too late, you still have potential to lose.