License(x) limits distribution till $ or time, -> GPL3.

Full version:
Please help me find a license, that allows for developer to monetize on his incremental contributions and at the same time, will automatically convert all his contributions to GPL3+ when a time line or a set bounty is hit.

Think of something like a copyleft propulsion license, that will allow developers earn money without ressorting to dual licensing or working on proprietary projects at daylight.

Currently, I think of some kind of middle-ware license.
This license applies only to said contributions. It is termination is time-limited and bounty cornered. Developer also has right to terminate it.
Upon termination, the said work is automatically transferred into GPL3+ license.

Technically, from GPL3 side, this requires that users who receive the non-freed contributions have not right to distribute them publicly.

Any ideas?