Usually a pedal point note is a Tonic or a Dominant note. Can we use the Subdominant note as a pedal point ? Should we use any note as a pedal point ?
Pedal points are usually on tonic or dominant notes, those being the strongest on any key. Usually they are the basis for the first harmony (chord), and will continue to sound through several other chords, usually dissonantly, finally resolving at the original chord.
They can be any note at all - it doesn't even have to be a diatonic note. Any note can be used. A pedal point is most often a rather low note, being named from the use of a pedal on an organ. Low notes (played one at a time) can sort of fit with many harmonies to provide a small excursion from the diatonics. It doesn't have to be a low note, though,as inverted pedal points prove.
See also double pedal, where two notes (usually tonic and dominant) are both held. Perhaps the forerunner of the 'power chord'..?