Idealistic and interesting, but too much manual human work required for such a system. And I cant imagine it being very reliable as far as block intervals and such go.
Well, at first I wrote the first post, and then deleted that, and then restored, FWIW.
If the task's period and also valuation period is set at certain definite intervals, then the task is to be done by some deadline, and also valuation by some deadline.
So, if we also consider, following the modern trends, that the tasks can be distributed as different blockchains, or sidechains, or each particular set of task to be a blockchain, or each particular performer has a related blockchain, then it would be like a blockhain network, where each blockchain will be functioning according to its own speed.