I like how Shadowbolt feels for the class in PvE; my personal preference is to have a cast-based nuke as my filler. I have a Shadow Priest (had, I re-spec'd her into Holy / Disc), and I didn't like the channeled nuke style of play. But that's just my preference.
I would feel very unhappy with my Affliction Warlock if I had to suddenly start playing her like I did my Shadow Priest. On the other hand, I also recognize that there are Warlock players who prefer the Drain Life-style as their filler. I want them to be able to have fun, just like I want to have my fun. It'd be pretty selfish of me to want it ONLY my way.
The issue with your argument is that there is already a shadowbolt spamming spec. Thats Demonology.
Corr = Corr
BoA = BoD
UA = Immolate
Haunt = HoG
Shadowbolt = Shadowbolt
Why do you believe it unfair for there to be one drain spec and one SB spec? Why do you consider it fair to have two specs for people who like Shadowbolts and none for those who want drains?
P.S. no, they will never make aff equally viable with 2 different fillers, not on purpose (it might happen by accident, as it is right now).