If the new forum is mobile-friendly, I think that will be the most significant feature to give it a slight push.
This... I literally had to buy a laptop
[I always preferred desktop] last week due to experiencing multiple power outages on a daily basis
[although there are a few workarounds while using mobile devices, it's still a big mess (even for just reading stuff)].
With all this in mind, do you believe that once the new forum is released, Bitcointalk will increase its userbase?
Yes, but I'm "only" referring to retaining most of its current users
[better retention rate], as opposed to attracting "more" new users.