too complicated
If you want to bet in favor of an event happening you buy the PM asset.
If you want to bet against you borrow and sell the PM asset.
It does not sound complicated, does it?
Even more so if it's wrapped in a good UI hiding away the underlying process.
The only concerns left are those two:
(1) the legal aspect (but I'm sure those PM assets can be issued by businesses registered in jurisdiction where this is not an issue)
(2) the issuer trust aspect (as is the case with all private bit-assets and UIAs)
Otherwise it's just a matter of time before someone does it and makes tons of money on it.