With all this in mind, do you believe that once the new forum is released, Bitcointalk will increase its userbase?
I think that the best part will be, as DdmrDdmr also pointed out, that major search engines should not punish bitcointalk any longer. This will bring (hopefully a constant flux of) new users with genuine interest in crypto.
The mobile-friendly part will be... a bonus

All in all, yes, I do believe that new forum software will help increase the user base.