That system is purely for players in the U.S., so I don't really see how that would be feasible or fair to players of other countries where there isn't an equivalent.
Plus, category titles in USCF aren't really that hard to get; Category 4, for example, mostly consists of players in the 1200-1400 range, though there are norms you do have to achieve for them. Chess.com doesn't even recognize NCM, so I doubt any of these would be considered, especially since titled players typically get lifetime diamond membership
USCF has titles like 4-category, 3-category, then 2-category, and the last one is 1-category.
I think you can create a blue line, similar to the title players, with a number like 4. Cat.