I was kind of in the same boat on this one. If they're so great why is hardly anyone producing or using them? In the end I think it all comes down to marketing. I think that HID is going the way of the dinosaur (but much slower) and when a company looks at whether they should produce the next big thing their choices are LED or Plasma. I think that Plasma may actually be the better of the two but it's not as profitable. With LED it's way easier to manipulate the marketing with different wattages/diodes/spectrum/lens angle/heat management and try to claim an edge. With Plasma they pretty much just work so how do you claim a competitive advantage. So the marketing machine chose LED and here we are.
Just my $.02
When you say "If they are so great, why is hardly anyone producing them". In the begining the opposite question could be asked about LED. If they were so bad, why was everybody producing them. Obvious answer, for a quick buck! In my personal opinion, LED's will have their place in the community when they dial in the proper wavelenghts. As far as I am aware, no specific research has been conducted as to what specific frequencies must be used for optimal growth. Every plant would be different to some degree, and then again for each strain, so until that has been assessed, LED's will suffer or at least until a broad spectrum unit is established and works well. Plasma on the other hand I believe in the not to distant future will cover most bases in relation to spectrum.
I dont know why hardly anybody is producing or using induction. I was completely unaware of this tech months ago until I stumbled accross it. One possibility is that due to the life time of the product, it had been scrapped by large retailers due to a one off purchase being sufficient?
Further, until now, I believe that high wattage units simply did not exist along with the ability to taylor the lights colour spectrum. All I know is that these Blue Dream are looking very good at this point and the lights have shown to work extremely well during vegitation just like T5's. So at minimum, having yet another option to veg plants with with a longer lasting life is just better for the community as a whole.
Plasma initially will take the same route as LED, all about spectrum frequency / colour / par. As yet, there is NO company producing Plasma specifically for growing that I know of. The light sources are being adapted for growing but not produced at the source for growing. That meaning that the spectrum at the moment is less than sufficient for flowering due to the massive lacking in red. If you look at Luxims LEP (Gavita and Stray Light) the light is exceptional, very broad spectrum (although lacking in red and intensity) This will change if the source is backed by the growing community as there are rumoured higher wattage units in development in the 600w range by Luxim for this year with a possible red puck early next. Definately interesting times ahead.