Built-In Preamp for Tube Mic

Here's something I've been wondering about for a while...I'm not too familiar with mic design so please bear with me  ;D

Why not build in a tube preamp into the power-supply box for a tube mic? Has this been done already? That way, the preamp section's input could be optimized to some degree for the microphone circuit's output. I think there would be other advantages to this design as well, but also some disadvantages.

One reason I was wondering about this is because I was reading about the "church mic" and also about the U47's that Rein Narma modified for Rudy Van Gelder's studio. In both of those cases, they made the output of the mic less hot so it would work with existing tube preamps. I was wondering how come they didn't hack a preamp into the power supply box.

Reo

you could build a mic power supply into a tube preamp but then you are kinda limited to one preamp for you mic, which sucks. I would not want that at all. Imagine if your stove was built into the walls of your kitchen, that would be great but if your stove breaks or you want a dual oven or a gas stove you would have to replace your whole kitchen.

well whatever, I'm not so good with analogies.  ;D

Building a preamp into the power supply box would be less than ideal in order to have a hum free signal. Having it external to the power supply (with it's hum inducing transformers) would make more sense. 
Many preamps have external power supplies.
Many people like to be able to control the level from the control room, not from the power supply out in the room.
If you want a higher level from the mic, you could add another gain stage in the mic, or use a level booster between the mic and control room.
If the level of the mic is too hot for a particular preamp, you need to pad down the level - but this anecdote was probably for fixed gain preamps of the older days. Maybe you just need to plug the mic straight into a line level input on your recording interface if it is hot?

I've thought about that too but in addition to noise and the other issues mentioned above, another big problem is demand.  These days, people using tube mics in studios usually have plenty of preamps.  People doing location recording are less likely to be using  just one or two tube mics.