Do accelerated abilities have specialities? The text in "Hedge Magic" infers that they are in all ways like regular abilities that advance as arts?
If so, then presumably Viktir (who's runes are accelerated abilities) presumably have a speciality for each of their runes?
I would argue that they probably shouldn't; in the sample characters in Hedge Magic runes get listed like Arts rather than Abilities. Likewise for other Accelerated Abilities like the powers of the Goetic Art in RoP: Infernal. Also, serf's Parma, but don't Methods and Powers on the sample characters in RoP: Divine and RoP: Infernal have specialties? They're basically what gets called Difficult Arts in later books, and they get listed like Abilities on the character sheet too.
In the saga where I play a Franciscan with Methods and Powers, we do allow specialties and I think that the description in RoP:D does specifically list appropriate specialties.
Personally, I think that it is OK since the advancement is so darn slow, having a narrow focus where you can add 2 to your "casting" total seems appropriate. Accelerated Abilites seem to have a narrower scope so maybe not in those cases.
Just my two cents.
They should do. They are Abilities.
Difficult Arts should not, because they are Arts.