I don't see how it's a problem; your rank is just a function of how many skill points you've allocated and when you reach the top rank there's still more skill points to earn. In other words, ranks aren't actually your level, they're just a label based on what your level (or equivalent) is. Adding more granularity to the top level label doesn't really get you any advantage, so I think it's best to keep it simple.
Plenty of MMOs do this sort of thing. Warhammer Online, for instance, has the game divided up into four tiers; the content you have access to depends on the tier. And what tier you're in depends on your level. It's really the same thing, just with different words. Furthermore, in STO they don't actually have to raise the "level" cap... just add more skills.