Mike Mearls explained on Twitter that monsters and traps will roll to hide against the players' passive perception checks. This feels better to me, since it still cuts down on rolling (the DM rolls once, instead of every player rolling every turn), but it's still random (so one extra point in Perception isn't the end-all-be-all).
That does make it less deterministic when building the environment, which is nice. However, the PC with the greatest passive perception check is still the source of all perception for the party in most circumstances. That is, anything a given PC can find the PC with greatest passive perception can also find, and anything the PC with greatest passive perception can't find can't be found by any PC with a lower passive perception. Conditions which would change that are:
1) Every trap (or whatever) rolls separately against every PC. I don't think that is what Mearls means, although for pre-designed areas it wouldn't be so bad on the DM. For improvisation, however, it is even worse than having all the players roll actively since the DM would have to do all the checks. One could combine these, I suppose: let players roll to get randomness for improvised hidden elements, and let the DM roll for things planned ahead of time. Some weird metagame issues might arise from that, though.
2) Only a subset of the party can passively perceive certain elements. For example, people must be in the "correct" part of the room or something. For certain tables that level of granularity might work, but as soon as the players have to start describing it, it seems a lot like active perception anyway.
3) Players have a wide variety of modifiers to passive perception to notice different kinds of things. So the elf spots secret doors and the ranger spots tracks, although in their own little domain of excellence that PC is never beat, which that doesn't feel much better to me.
4) Every player rolls against each thing, but of course that is what passive perception is trying to avoid in the first place. Even with pre-rolls this becomes laborious.
5) Players roll "passive" perception, but only occasionally.
In my homebrew I've played around with the idea of "scene perception", which is based on that last one. The DM rolls a passive perception check beforehand for each PC, against either a fixed or random DC for some hidden element. However, that PC's roll applies to everything in that scene, where the boundaries of a scene are basically up to the DM. (In a dungeon that might be per room, for example. My current rule-of-thumb is that if the environment or circumstance changes significantly, it's a new scene/encounter with respect to perception.) Thus, in any given scene the DM usually knows beforehand what a player can perceive, and improvised elements fit in seamlessly with no or little additional rolling. From scene-to-scene, however, which PC perceives best changes in a way the party can't predict. This approach could mesh well with active perception checks against single elements, and maybe there could be some resource-intensive way a player could "refresh" their passive perception for an entire scene.
My hope is that it can be combined cleanly with "scene concealment" to find a middle ground between static passivity and the grind (and well-known inevitabilities) of a billion opposed checks. Sneaking around (or even deception in social encounters) would involve a similar passive check and optionally utilizing circumstantial modifiers in the environment to increase it. One might be able to take actions to improve things for a round, but that limits mobility, etc. Unlike perception, however, sneaking characters usually know they're sneaking against something, and since that means such a scene is less likely to feel like a waste of time at the end, concealment can probably afford to be a little more active than perception.
Simple encounters could remain quite abstract, relying solely on passive checks to keep things moving. More complex ones could be a bit more like combat, in which case the passive checks set the stage in a way somewhat akin to initiative.
