gruvbox is open source project
I believe there are enough forks at the github and you're free to maintain your own
As it's distributed under MIT license I feel like you have no restrictions to do so
However gruvbox was started as a personal project and was maintained in my own tempo and according to my personal taste
At the moment I think that adding maintainers is not what I would like to see
No offence
Due to this statement:
Originally posted by @morhetz in https://github.com/morhetz/gruvbox/pull/206#issuecomment-475966990
Propose to collect alternative, actively maintained color schemes. And perhaps adding them to WiKi pages.