We could do a tube PSU but I really don't see the point. Semiconductors are just much better suited for this role and using tubes is very wasteful of energy at the levels we operate at. It also sets us limits as these parts have hard design limits which shouldn't be exceeded or you end up with the arcy-sparky of the Woo amps. Then there is the whole issue of how to design such a supply. A tube rectifier with a R-C-R-C- etc. string isn't something we would ever do and a fully regulated tube supply is very costly and complicated. More heater lines to worry about too as if something like the Megatron didn't have enough of them already...
I'm not going to say we'll never do one though as we are all over the place these days. Hell, I'm working on a SET Stax amp and if somebody would have suggested we'd use a tube CCS for an EL34 last year I would have laughed in their face.
It's funny how the mere act of trying to fix something that's fundamentally broken such as the B-10 can spark some truly great ideas...