This thought experiment took part in a world where the web was significantly worse than our own: hoards of malicious AI's and precious few humans trying to not be mistaken for a malicious AI. Of course a pre-existing trust relationship is much better, but ideally there'd be a way for untrusted authors to make it through to a real human somehow. Attaching money to the commit would be one way to do that.
Similarly, betting that a public figure will still be alive a month from now is functionally equivalent to putting out a hit on him.
As far as using prediction markets to put a hit out on people... How does that differ from how it's done now, except that the flow of money becomes part of public record where it's more likely to appear as evidence against you in court?
Anyhow, like most online media, moderation will be necessary. If we can't game-theory our way to a nice solution, we can just do the normal thing and ban the activity we don't like. I just think that where possible, designs that align incentives are likely to be more successful. Prohibition is generally ineffective, expensive to maintain, or both.
In the case where you're betting heavily in favor of a commit, maybe because you've reviewed it and think it's good, maybe because it contains malware you want to inject... you'd be attracting reviewer attention to that commit because if they can talk the maintainers out of it they end up with more of your money.
Probably the best strategy for a malicious committer would be to sneak through a low value nothing-to-see-here commit, because the low bet would not attract extra reviewer attention, so the maintainers have to set it high enough that it still incentivizes review.
I don't want to live in this world, by the way, I'm just afraid we might have to.
I imagine a hard problem is building a system to resolve these markets.
For instance, if you spot malware in a commit you could bet heavily against it being merged, and that would attract the maintainers' attention, and they'll see what you see and not merge it, and you get paid for the code review--that money would come from whoever bet that it would get merged, which you could require be the author of the malware. I haven't worked it out entirely but it seems that there are opportunities to build games that reward dilligence and transparency and penalize deception and spam.