Crazy Jerome
First Post
I think we have a difference in semantics here. To me "Theater of the Mind" refers to pure imagination, with mechanics that use real-world measurements. The way non-minis combat in DnD has traditionally worked.
Abstract positioning and zone systems are a very different matter, and I suspect, very foreign to most DnD players. If a zone system exists in 5E, I have to expect it'll be a module sitting next to the grid module.
Yes, that is a difference in semantics. To me, "TotM" means "In our heads, not on the table." Then either system can be relatively simple or complex, abstract or specific. That complexity in TotM or grid often take different paths is only because most game writers have some sense of what will work.

Setting that aside, consider this: "Push 1 square" is changed to "Knocked back 5 feet." That's a change to create an illusion geared towards TotM, but it doesn't really accomplish much outside of whatever the illusion itself does for people. It might appear marginally more precise to some people, but if the game does all such movement in 5' increments, it isn't even that in reality. As such, it's really a grid mechanic expressed as a TotM mechanic. This is because in 4E (and D&D in general), the advantage of getting someone to forcibly move is in whatever you move them into.
However, assume for a moment that we have a good mechanic that models something like "breathing space"--where a short retreat or pushing your foes out of immediate melee range gives you a second or two to reset your defenses and orient yourself to the situation. Nevermind exactly how it works, as I don't want to get bogged down in objections to the details. It's a valid concept, albeit one that D&D hasn't really supported before. Perhaps there is also another supporting bit where so moving someone is causing them to interfere with other attackers, when outnumbered--also a valid concept that D&D hasn't supported.
Now, regardless of how it is worded, "knocking someone back" is a useful concept--on the grid or off. If you happen to knock them back into a fire, that is helpful too, but not the main purpose. If knocking them off the edge of a building or cliff face is possible, it isn't that hard even in the TotM to establish that you and the opponent are so placed.
This is the kind of thing that I think they really mean by an agnostic mechanic. It has slightly different flavor and emphasis on grid or off, but it is roughly useful in both.