Versions of #4 have worked, though not usually structured as X% of all future earnings. The most common version is the group-of-freelancers variant, where a group of people are really working independently, but do it legally via a partnership, which pools income to reduce risk, share upsides, smooth cash-flow bumps, etc. It's pretty well-established in a number of professions outside tech, e.g. in law, a partnership…
A workers co-op is a good alternative to a partnership if your jurisdiction has sane laws. (in other words if you're not in the United States).
The big downside to partnerships is that you're exposed to unlimited liability.