I actually hacked together an almost functional system similar to this a few years ago. It used the same primitives, delayedAssign and parallel::mcparallel, to implement parallel-evaluated lazy promises. It was nearly useful, but I couldn't get it to work when passing one promised value to another lazy expression, presumably because only the process that forked a subprocess can read the value it returns, so the second forked process can't evaluate the promose. It looks like this package solves that problem by forcing evaluation of any implicit futures before passing them to another future. I'm definitely interested in trying this out.