I know at least two people that are both eager and capable to bring OpenPilot to Model 3/Y. The good part is that I can help (and already promised them that), as I know most of the CAN messages needed for integration. The bad part is I do not have an M3/MY to test on. If you want to loan me one for few weeks, do message me and I might have a full working version shortlyafter that.
Why would you want OpenPilot on a M3/MY? In case you did not spend the 12k on FSD but you want to have more than just the basic lane keep. Because the future that OpenPilot can offer (faster than the much promised FSD), while is not as complete as dropping your car anywhere in the world and driving itself back to you, is more realistic and will happen a lot faster.
This will not be an easy integration. Model 3/Y (AP3 hardware similar to the one on the latest Model S/X) use a private CAN bus that duplicates critical messages from the chassis bus. So, in order to even have basic lane keep assist, one will need a Comma three plus at least 1 additional Black Panda to be able to control effectively both CAN busses in sync.