Class D is one thing, but digital modeling? Sure, it might sound good, I work in Logic, I use and like a lot of the plugins, but as far as my understanding goes, it can never exactly be the same as analog produced audio, if for nothing more than the fact that analog is a continuous time-signal/continuous fluctuation of electric voltage, whereas digitial is a discrete time-signal, in which the continuous time-signal of an analog input is approximated, and each original sample value is repalced (quantitization). This process, given it's only an approximation, loses information. While the Nyquist Theorem does allow for the possibility of perfect reconstruction of the sampled signal, while with high enough sample rates and bit-depths you can hide aliasing (or with a low-pass filter), the point is that a digital signal simple is not the same as an analog one.
So, digital sample can be good, that's fine for some people, but to claim it can do exactly what a tube amp does? Well, then I guess you can get into the whole "well functionally there's no difference" and I don't think anyone is going to win that argument. But what I WILL say is that part of the reason people prefer analog has been shown to be its technicaly limitations and defeciencies, which can introduce inaccuracies and variables (what people might refer to in vinyl as warmth). This can be the explanation regarding why no two amps of the same model, with the same components will necessarily sound the same. There are so many pieces of the puzzle which are interacting, and possibly deteriorating in real time, that to say a digital model can perfectly capture this is silly. It would have to be modeling so many individual parts of the signal chain, dynamically altering them as they interacted, and as far as I'm aware, there aren't any modeling amps doing that at the moment. As I believe Jimmy mentioned, modeling amps can capture a good portrait of what an amp may sound like mic'd and recorded, but that's not the same thing. And I'm not just talking about valve amps here, but all analog amplification.
My question is, WHY does it seem to be the goal for so many SS amps now to try to emulate a tube sound? I don't think Kustoms or Acoustics or other early SS amps were striving for this, and I don't know, but personally, I prefer what they sound like to more a lot of recent SS amps (maybe its component drift, and these amps not all being kept up to snuff or something along the lines of what I was saying above about people's preference for analog). Someone I guess could say this is just "vintage adoration", saying it's better simply because it's old, but I just appreciate what they're doing for what it is: providing a different tonal palatte. I'm more of the mind of use the tool for the job. If that job requires tubes, use them, if it requires a SS amp, use one. I guess I just don't get the hold idea of trying to make something sound like something it fundamentally isn't.
I can see a trend for maybe getting back into 100 watt class tube amps ... With more sane stage volumes, brought on by more and better FOH setups amps like the V4B into the matching 2x12 makes some sense in the present day world. After years of using micros and neos I have made a slight return to an all tube rig for certain select gigs. I can't see ever going back to them as a full time thing, and personally have no interest in hauling the big tube classic rigs around ... Smaller, lighter, and cheaper dollar per watt is where I see the mainstream of bass rigs going.
I've been using 120w amps for years now, though it's not so much for more reasonable stage volumes, but rather so I can crank them into slight power tube breakup. But I DO like seeing the return to lower watt tube heads in general, or rather a move away from wildly extavagently powered amps in general (not to say I don't think a 400w tube amp isn't something truly amazing). What I'd also like to see with this move away from higher power is a similar movement in speakers away from hilarious power handling to more effecient speakers, necessitating less power but being able to put out more SPLs. I'm refering to speakers more in the vein of old JBLs, lower power ratings, higher efficiency, and personally I think better tonal characteristics. Will it happen? I doubt it, but I'd like to see it.
Whenever we as musicians break things down to "Can the audience notice in a live setting" we are setting the bar way to low.
I think this is a very important point. Sure, it's the audience that you're performing for, and while the vast majority may not be able to tell, when did we start striving for the lowest common demoninator? There's going to be other musicians in that audience probably, maybe think about playing for them, or god forbid, yourself. You can put on a good show, sound great to yourself, and at the same time sound good to the audience. Whether they all notice shouldn't be the point, but whether those who care to notice can should be the point.