First of all, IMHO, I'll agree with the sentiment that the OP likes pumping the NOX. I've seen it on other threads. I'm not sure why, and don't care why, but I do find it mildly annoying. I came to that conclusion independently and before this thread. I'm not sure the point of pumping a particular make unless you work for Minelab and have an economic interest in their success, but whatever. JMO. (One would think one would do the opposite; what is to be gained by telling your competition what the best machine is? The silvers are being pulled, and they ain't coming back. Let your competition learn on their own. I certainly don't mind being helpful to newbies, but I don't divulge all my secrets).
So, I'll chime in with a gentle "stop pumping the NOX" request. Some here are growing weary of it. We know you have a NOX, and think it is wonderful. Move on, that fact is uninteresting.
Second, I'm not sure of the overall point of the thread. "Innovate or die" has been the rule since the first stone tool was invented. It is no different in the detector business, and it certainly didn't start with Garrett and the AT Pro. Anyone remember when the introduction of the DD coil was a big deal, for example?
Third, IMHO, the juice has pretty much been squeezed from the VLF orange. I think these new machines are finding a handful of coins on the margin not because they are better, but because they are different. Run any new or different machine in a hunted out park, and you will find silvers the previous folks missed simply because the signal processing is different. A particular coin at a particular angle next to a particular piece of trash will be missed forever until ice or rodents push it around, or a new signal processing algorithm comes along. But, I guarantee you that new algorithm will miss other things the incumbent machines will find. The thing is, they have already found it. I think that is what is being seen, but we'll see. I have on my list for next year some unbiased comparisons of several machines to determine if they are actually better.
Mutli frequency was a big deal, and people, including myself, were pulling silvers out of hunted out parks by the wheelbarrow full. But multi frequency was forever ago as these things go. Nothing new under the sun in the VLF world IMHO, different signal processing, faster processors, but no paradigm shift like the DD coil or FBS.
So, what is really next? Who knows, but the root problem with VLF technology, IMHO, as the deeper you go, you simply can't overcome the ambient mineralization (note that both DD and FBS were invented to attack this problem). NOX may find a silver next to a nail (so will the E-Trac, if you know what you are doing; you should see the number of rust-stained silvers I've found), but is any new VLF machine addressing the mineralization problem in a new way?
I don't think so, because VLF by its very nature is hamstrung by it.
So, IMHO, to try to answer the OP's question, the arms race will be furthered by non VLF technology in consumer machines. I'm thinking sonar (think ultrasound), but it could be anything. I'm an economist, not a physicist but have some background in physics, so I know enough to sound like an idiot to those who really know their stuff
We'll see, but I don't think VLF will ever find half dimes at 12 inches, but I think they are down there, and I think a technology that is not hounded by mineralization will find them.