Yeah, it is just a matter of working out what the mechanical details are. I mean, I think various supers games have done similar things. Superheroes pretty much fall into a small set of bands, from 'ordinary human' up through 'very talented ordinary human', and on into 'super powered', 'really super', and 'ultra powerful'. I guess you can argue who falls into which of those bins, but your design would basically be about the same thing.
I was actually thinking about this the other day. I mean, there's an argument that says you only really need 1 or 2 story arcs per tier, and 3 tiers definitely seems like the 'sweet spot'. You could do all of that in 5 levels (with epic getting shortened to 2 levels). Each level would be one story arc, nice and simple. Finish it up, level up, go on to another one. Such a game does assume a fairly rapid pace of advancement though, assuming you play reasonably often. Even if each story is 3 sessions long, that's only 15 sessions, maybe 6 months if you skip some weeks. You could stretch it to 5 sessions each without too much trouble, that would give you maybe up to a year of play. For ME that would be more than enough, but there are many who really like to both progress fairly often, and yet play a much longer campaign. Granted, they often don't actually run them through to the end.
So, maybe the idea of 'progression' should be altered. Currently it is level based in D&D, but you could create a system that isn't. My own game runs on 'boons' for example, where you gain a level when you achieve a treasure (which is basically a goal since 'treasure' is a very loose idea). It is the boons that actually carry the new character abilities. All levels are doing in my game is adding hit points, etc. (as in 4e). You could ditch the labels of 'level' and just have every 'power up' be part of some boon (treasure). That might be interesting. Tiers would become more implicit, but you could still work something out there.