During porting from D7 to D8 there are some points that would be really helpful to follow in order to work with other contributors during porting timeline.
- Add comments to D7 module copy about some specific part already ported to D8. This can help others not to interfere with your work.
- Create Change Record at Drupal.org . e.g for dmaps project about how code was used on D7 and how it should be converted to D8. It can help others to port dependent modules easily.