Just to throw this out there, but how about constructing the incentives of the world such that players will actually tailor the game to themselves?

Like, if I take the discussion about those three encounter types, I'd say that you can tailor it but that Quertus' idea of just making it so the encounters span that already isn't going to work when the abilities people have become very diverse. If we're talking about dealing fire damage, sure. But what if we're talking about the ability to see the connections between events and the people who caused them, the ability to impose a new natural law upon reality within a 1km radius of a ritual site, or the ability to change the taste of food to anything (including things that aren't tastes).

It seems clear to me that a random sampling from pretty much any kind of distribution of encounters isn't going to really span all those bases. But at the same time, it seems clear to me that this is often not actually a problem in play because (experienced) players with very open-ended powers will seek out opportunities to make them relevant.

However, that only really covers the first of Jay R's types of encounters. So shouldn't the question then be, how could one incentivize players to actively seek out situations in which their particular powers would not necessarily provide easy solutions, while at the same time making those incentives make sense in an overall world structure?

The natural result of this is of course going to be tailor-making things for the players, because when the players seek out particular opportunities to explore in greater depth they force you to spend correspondingly more time generating that type of thing. But its in contrast to tailor-making things from an external perspective of 'I'd better make sure you can solve this quest' since its directly connected with the players' activities within the game.