maybe this just silly wondering, but is there something why not to use singlereedtype with regulators..like samekind they use with finnish/swedish säckpipa or estonian torupill chanters
length of reg body ? sound?volume?
well its an honest question; and yes, it’s because of length, timbre and volume, that it would be a difficult, if not worthless goal. I dont play the Baltic & Scandanavian pipes you mention, but I do play Italian pipes: many of these operate with single reed in a conical bore, & like the uilleann reg play exclusively 4- 5, or 6 pitches, and never jump the octave like an ornery UP reg reed. at least in my experience.
Having said that, these chanters are longer than UP regs, because they are built on a diferent portion of the harmonic air column. (for ex: the “fa# sol-la-si-do” ritta chanter is approx 17" long; the corresponding “fa# sol-la-si-do” tenor reg is 12", give or take.), also have a far more conical bore, making them louder.
The only closed bore single reed pipe chanter I can think of would be the Bulgarian Gaida when played ‘on-the-knee’. My Gaida has the angled bore: im certain somoene else on C&F could shed more light on that aspect.
Lastly, if some as yet unknown brilliant, compelled, yet seriously twisted individual finally deciphers a way to make a single blade reg reed; more than likely it’s timbre would mesh too closely with the drones timbre, making it difficult to discern aurally, or blend in an overall sound as do regular double reed reg reeds 
In my opinion, of course.