Since what used to be mid-tier seemed to all but vanish, I am good with triple I standing for the former midtier title. I take it as an indie developed game, or a small internal studio that us part if a company that hit it bug. I would use this thread to flesh out the meaning.
I take Cuphead as one example and Minecraft as another.
I would go with triple I because the games originate from small studios
Even No Man's Sky can be argued to be a triple I title.