On a sunny day (Mon, 07 May 2012 09:00:45 -0700) it happened John Larkin wrote in : o why not a depletion mode device and be done with the problem?
I see an other problem with using a MOSFET that is normally 'on' as a series regulator.
Suppose you just suddenly connect the full input voltage, then the thing conducts and destroys anything connected to it. It would put big limitations on input rise time, output capacitor and load, input capacitor, I would not want one. I have use PNP series many times, even in the latest tritium PIC project 2x, but those are not 'normally on'. Or did I misunderstand the question?