If you both believe in the project but your project implies a cultural change, then it is best that you part ways with an agreement to share the code developed

If you both believe in the project but your project implies a cultural change, then it is best that you part ways with an agreement to share the code developed until now, and the relationships developed until now, and work on your forks from now on without sharing anymore. This way there will be two companies trying to evangelize the prospects (sometimes the same) with the need for a huge cultural change. Your smallest problem will be competition from your former company, compared with customers not even considering your solution because they feel it is an overkill.