What do you think, is my idea legal regarding your license and OK to you?"
I don't a problem with this, changing your fork license from (MIT License) to (GPL) is not a problem for me
(1) You are doing extra work and your free to set the license of your extra work
(2) You already did nice contributions to the Ring project, and your work in other forks will be useful for the community too
(3) Since we have the original Ring implementation under MIT License, Having other options with different licenses is a (+), i.e. very nice
Greetings,
Mahmoud