Definitely not a waste of time.
1. If the C65 ROM gets open sourced tomorrow, we have several routines we can transplant to improve the original ROMs.
2. This project is not just for Mega65. I really want to have a Kernal for my Ultimate 64 which can talk both JiffyDOS and DolphinDOS without ROM switching, for now ours is the only one capable of doing so. Main problem is the compatibility, which is not too good as of yet.
3. I'm having fun working on it.
Also don't forget that the OpenROMs solve the legal uncertainty for emulators to include a working ROM set.
It all depends on the rate of compability.
Besides the own "fun working on it" it could be frustrating, if some people works much on a OpenROM and then 99% of all Mega65 buyers uses the original ROMs because of 100% compabitily. So all the work for the OpenROMs was just for "own fun".