Ask HN: How should vesting work for a side project?

I'm starting to work with a friend on a side project and trying to figure out how to handle vesting.

If it were a typical "quit our jobs, startup or bust" plan, I think we'd both be okay with the typical 50-50-or-close-to-it with 4 year vest and a 1 year cliff.

But this might stay a side project (even if it's profitable) indefinitely. We might both be okay with that, we might both want to turn it into something bigger, or one us might want to turn it into something bigger but the other one doesn't.

Is there a way to handle part-time vesting that's better than just a cliff since neither of us is sure we want to jump?