I think you are greatly underestimating the cost and complexity of setting up a tube manufacturing facility. It's also not a 'green' business which adds to the cost. Who is making tube manufacturing equipment now? When the Brits got out of tube manufacturing, they sold their equipment to the Chinese and it has taken the Chinese many years to produce tubes that people actually wanted to own. I believe that Richardson Electronics has bought up some of the tube manufacturing gear from American companies as they went out of the tube business. I believe the last American tube company that went out of production was the MPD plant in Owensboro, KY, that made 6550s (formally the GE plant). I believe that Richardson has all of that gear in storage somewhere in Illinois.
Remember that Western Electric tried to put their 300B back into production and they had the advantage of having the original equipment, drawings, specifications, and the doping recipe for the cathodes. It still kicked their ass and during the limited time the new 300Bs were in production, I didn't hear of anyone claiming they were better than the original 300B tubes.
What college is turning out vacuum tube engineers? There are a very limited number who train for the microwave tube industry which is entirely different than the audio tube world. So even though you say it's a well-defined art and process, the original tube companies haven't made their production processes available to anyone to my knowledge and it might as well be a black art. If it was easy to start up an audio tube company, it would have already happened in the U.S. There is a world-wide demand for vacuum tubes for both audio gear and guitar amps, certainly enough to build a business case if one was so inclined to jump in. It's a daunting challenge which would need some very deep pockets. It could take two or more years before you could have acceptable quality tubes that you could sell on the market once you started production.
