Is it feasible to design a blockchain based system that signs inputs and outputs of an agricultural enterprise and pays out chain investors (in-kind, suppliers, labourers, land owners, etc) with a contracted fixed, per-unit price plus a bonus based on the success of the venture?

I think so.

The already existing frameworks based on Ethereum are already able to provide the underlying framework for any design. Smart contracts can be built to serve up front payment of a set rate, generally lower than the normal market price , with a dividend of sorts paid out upon the closing of the contract.

Next step?

I need to dive into Ethereum again and see who is generating the tools that lend themselves to attaching blockchains to real world production.