It would be nice if there were some third party that companies could turn over the results of these interview project assignments to, which would allow release of that information to other companies upon authorization by the candidate.
The idea is that you interview at some place that asks for a substantial take-home interview project. You do it. Afterwards, the project requirements and your solution are turned over to third party.
Then the next place you interview wants a project, too. You can point them at the third party and authorize release of your info to them. They can then see what that first company asked for, see what you provided, and if it covers the same kind of things that their project does they might then accept it instead of making you do another one.