I agree with Mullins in the sense that for experienced and top level divers, the key is consistency. They would/should pretty much know what they're capable of, within a range of some 5m. With the exception of maybe Herbert (who I believe proposed this in Sharm), they'd probably end up diving just as deep, nomination or no nomination (and in the end I would guess Herbert too, it's hard to say when he's being serious).
But for intermediate divers, who have "good days and bad days",who's performance varies greatly and big gains can be made by simply "pushing it", this type of "no nomination" rule would give a big benefit - and also IMO a very big risk. The difference could be tens of meters and I don't even want to imagine what the dives would look like (kick, check cauge, kick, kick, check, kick...ok that's it, sprint to the surface)
It's an interesting idea but I don't think we're quite ready for it in larger scale, nor will we probably ever be. I think much more feasible and useful would be the kind of 5m "grace zone" that was in the rules briefly a few years back. Meaning, you still nominate a depth, you still "switch off and wait for the bottom" (which I too think is an essential part of deep diving - not needing to be constantly aware of the depth but simply waiting for the plate). But you don't get huge penalty for missing the target.
Or just adjusting the penalties a little. Maybe something like -1 for not bringing the tag and then -1 for every 5 meters missed?
But I do think this concept could work and even be fun in controlled situations...With a good understanding between the divers and the organizer, maybe as some sort on "invitation only" type of thing. And it would be great fun to watch.
Kind of like the static invitational in Monaco in 2005. That's why I also suggested "elimination rounds" with 2 divers starting simultaneously

That was exciting to watch even through a very blurry internet video with weird time leaps.