August 2023 update. City Of Costa Mesa does not allow any short term rentals, even hosted rentals are not allowed.
I have this information in writing from the city direct.
The good news is that I talk to the largest STR property management company in the area and they say Costa mesa normally follows Newport regulations which does allow short term rental permits, and the city of Costa Mesa should be addressing this subject within the next 6 to 24 months
The city keeps rolling the subject to the next meeting, so no accurate timeline of when it will be addressed.