I'm almost wanting to say "nothing."
Over the years it seems like every attempt eventually gets too complicated to run.
In theory I think the best example I have seen is City of Mist - but I don't own it yet, I own another game in the same line: Legend in the Mist, so this is based on an assumption that it would hold up. It's very rules light with no stats or numbers to things, just tags a lot of narrative roleplay.
And that's where the elusive solution, should it ever be found, would lie.
A system without numeric definition to things and without tactical combat. You need to describe everything in terms of narrative dramatic flow. Like a comic book.
That's the only way to have radically different scales in play, and keep them all story relevant. It's also the only way to allow "anything" without trying to detail out "everything".
Super Hero RPGs have been my main thing for most of my time in this hobby - starting in 83 when I found Autoduel Champions in looking for a supplement to Car Wars. I've tried a lot of different games, I've spent years running several of them. Some of them held up better than others. Some worked in their early editions, and then got too complicated. But even that was only when we limited our idea of a super hero to something fitting the game mechanics. In that regard even Silver Age Sentinels was too pre-defined and it's probably one of the looser flowing games I'd GM'd.
So right now I'm thinking the answer is very close to City of Mist - but maybe not exactly where that is as that is, I believe, tailored to a specific narrow sub-genre. However it may be circling around the impossible answer.
