At first thought bga-only sounds bad but in reality especially considering the progress (or lack thereof) in CPU performance, a platform will be outdated anyway before you need a new CPU.
I still have a lynnfield and if I upgrade it will be a new display and new GPU.
I'd venture a guess to say that for 98% of the desktop space, BGA-only is simply not an issue.
The absolute number of people who actually replace their processor without replacing their mobo is going to be a rather small number I suspect.
The bigger (IMO) issue is going to be the mobo makers, as their job of selling enthusiasts on high-end $300+ mobo's which can't have the processor removed/swapped is going to be a real buzz-kill and will cast a pall over that entire lucrative market segment.
I own both a $350 Asus ROG MIVE-Z and a $230 Asus ROG CVFZ, but if that MIVE-Z came with a soldered-on CPU which couldn't be swapped out with another "play cpu" then I would simply not have bought it.
They may as well solder-on the ram while they are at it, or solder the SSD straight to the mobo for all it matters at that point. (which IS how the whole smartphone/tablet/pad industry works, so that may just be the future of desktops too)
But those $60 mobos or $100 mobos that get bought in volumes, a soldered-on CPU isn't really going to put a damper on that market segment.