Ok guys. Since everyone is being intellectual about this topic, I'm going to throw my 2 cents in here. This is based purely on MY experience with the Kemper, but given that I'm an average guy it would probably apply to most.
The Kemper is a phenomenal tool. To me, it captures 90% of the tone AND feel of the real amp. That said, it is not a Tube Amp Killer for the simple reason that the number of variations that are possible between signal chain, effects, settings etc. for any given amp are limitless. In that regard, it's no more a Tube Amp Killer than it is a Microphone or Mic Pre Killer. Simply from personal experience, I can tell you that creating a profile is very much a matter of personal taste. I don't like most other profiles that I hear. Not because they're bad, but because they don't suit me.
Like many folks, I bought the Kemper thinking it would be the Be All End All and I'd never ever need another tube amp as long as I live. The result was I became so addicted to profiling that I've been buying MORE amps and pedals than ever! Guess what?! All this led me to start selling profiles with the intention of funding more gear to profile. So how in the world would that adversely affect the amp market exactly? It doesn't!
Here's the thing. Amp manufacturers are a particular brand of nuts. They're secretive about how they got their "special sauce" and time and time again, when folks dissect and reverse-engineer legendary amps they often find that the "11 herbs and spices" are nothing more than salt and pepper and a bunch of bullshit. What I'm saying is there's nothing particularly innovative about tube amps and there hasn't been in 30 years. They all know that and they're afraid that modelers and profilers will ruin them. Instead of fearing this technology, they need to figure out a way to embrace it. If I was a successful amp manufacturer, I would be asking myself "How can I leverage this technology". I wouldn't be too nervous because "Tube Purists" will always buy the amp, broke musicians will never be able to afford the amp and the guys who profile will all want to get the real deal to create their take on it. Don't get me wrong, there will always be unscrupulous people who abuse return policies but that will ultimately bite them in the ass. We've all shipped amps and we all know it's a hassle. I wouldn't want that to be 50% of my business. Also, I really doubt that anyone is retiring on their vast Kemper Profiling Empire any time soon. There's simply no meaningful money to be made from profiling so to take on the financial risk of buying a $3500 Friedman BE100 with the intention of profiling it and returning it seems very risky to me.
In short, I don't know why the amp market is in a state of decline or if this is even the case. Look around this forum. Go into the "Post Your Rig" thread that YngZakLynch started. There's rigs in there that would make arena headliners jealous! At any given time, there's 3-4 Friedman threads on this board. So if amp sales are plunging, it's surely NOT because of modelers or the Kemper. I would hazard a guess that it has to do more with the economy(less disposable income), lack of interest in guitar-based music and the fact that the price of amps has gone up drastically in the last several years. I remember not too long ago, $2500 would get you a boutique amp. Now it gets you a Mesa LOL
Anyway, that's my take