Something equivalent to LIBOR rates could in principle be made to run on distributed markets with a great deal of transparency and little possibility for manipulation. They are a standard feature of many contracts. Whole central banks could be automated. Something like "next year's tomato quality" will obviously need a physical world mediator, but that's hardly surprising.
When the great recession started, it was not caused by an external shock, rather by the viral mistrust that the underwriters of the bad loans were solvent. A financial fragility problem that the blockchain can work to address.
It's that plus a whole new crop of perverse incentives which arise with any "smart contract". Especially, no smart control can reach out to the "real world" and get data, more less facts. A smart control would essentially be limited to some data-stream in on Internet. And anything like that can be subverted seven ways from Sunday. Do you really want billions riding on THAT?
(and, yes, give us some Rube Goldberg scheme of averaging six different weather stations for your result. I'm sure nothing can go wrong with any of those ideas. Yeah, World finance then gets to be hoisted on the lpad petard).