There is a misconception that was spread at some point. Official conversion is not a part of the sponsorship program.
There is no strict criteria for when we decide we want to integrate a mod into official. We have a quality expectation and we have to assess the time and work necessary to integrate it, do any necessary polish, fix issues, balance if needed. Official integration isn't limited to the sponsored mods. Any mod on the workshop could be offered to become official, but not every mod is suitable for integration into the base game... where it will be forced upon every single player.
Sponsorship allows us to support mods that we think are doing really cool things, even if those mods would never be suitable for official integration.