You know, this sounds kind of bad, but I have to think what if the OEMs like ASUS and others will still offer aftermarket motherboards? I mean, how OFTEN do CPUs explode these days that requires replacing? Sure, you can argue that it prevents simple upgrading, but we're living in an era where technology shifts literally every 6-12 months. Intel has new and different sockets pretty constantly, AMD does too, except they try to make the effort to take advantage of a new socket type for a while; just take a look at AM3+. FM1 is an exception, but they will be making a new APU for the FM2 socket for at least another generation or two of APUs.
Then take a look at how LONG we keep our hardware. Some here have had their i7s since they first came to the market and don't need to upgrade anytime soon. Really, the needed upgrade for PCs generally will be RAM or video cards than anything. So theoretically, if that person that rebuilt their system when the i7 first came out, and rebuild in a few years from now, they WILL HAVE to buy a new motherboard, new CPU, and possibly new DDR4 RAM; maybe a new PSU or video card(s) regardless. With a CPU soldered on board, it just eliminates a step of installation and possibly might filter down some CPU options that are getting to the point of being superfluous. How many different i3, i5, and i7 versions are there right now? Quite a bit.
It might just make upgrading more easier. Although, OEMs and Intel, and AMD, need to play nice in offering decent options though. Intel can't take full control of things nor AMD. It's kind of with GPUs, NVIDIA and AMD both make the dies and cards, but they also sell the dies to OEMs manufacturers to build better enclosures, heatsinks, and tweak around with settings to take full advantage of the chip. You don't upgrade the GPU chip on a video card, you upgrade the whole thing to a new one when it's not powering things well enough. Same goes with puter systems, you can't always upgrade the CPU on an older motherboard and expect great gains, you swap out for new parts.