I understand your points, but I'll offer a rebuttal to the concerns you mention.
Desktops don't beat laptops dollar for dollar, not for OEM products, because desktops are not portable while laptops are and that has nothing to do with the hardware and software included in the product. You would have to add a huge premium markup to desktop price to do such a comparions (e.g., double the price) and even then the desktop would not actually be portable. As I said in the original post, these observations exclude people who want to take a chance at building their own machine (taking a chance due to no warranty on the work and needing to fix anything wrong themselves).
Just fyi, heat isn't a concern for gaming laptops, at least not anymore than desktops, because they are specifically designed with the gaming needs in mind. This is true for any high-end laptop that is intended to do high-end work such as video processing. Heat is only a concern if the hardware is pushed beyond its intended limits for extended periods (e.g., trying to run demanding software or do demanding high-end work on a PC that is only intended for general use such as office documents and email). To offer a different comparison, heat is no more an issue for high-end gaming laptops than it is for consoles of the past and current generations.
As you mentioned, no one is going to be playing games (not demanding games, that is) or do any other high-end work using only the battery, or at least not for long. In fact, that's one of the huge areas of research (new battery designs and squeezing more life out of current designs). It has become even more of a profitable research area with the increased use of mobile devices.
Most people do not upgrade desktops, either, so that isn't really a concern except (again) for people who want to actually build a PC. There are far more users of PCs than those who wish to build and use them, after all. For most users, choosing to upgrade would mean taking it to a shop and paying to have the work done. Most people simply don't bother especially when the price of their current machine plus an upgrade would be about the same as simply buying a new machine. There's little point, and having an extra machine (or several) is usually useful. They can give the old machine to friends or family who don't have one or want to upgrade, etc., so it works out well for everyone, at least currently.
All of these points are elements for the OP to consider. Obviously, if the OP wishes to build a machine on their own, these points take a backseat to the fact that such a custom machine won't have any warranty for the work (aside from the individual parts warranties).
Edit:
I forgot to mention this, but Gstaff states on the new Bethesda Twitchworks video that they cannot reveal PC requirements yet but will do so closer to the game's release, implying that it will be stated clearly sometime before the actual release. One would think that it will probably be stated a few weeks earlier as well as posted on retailer and etailer sites. I seriously doubt that they wait until the very last minute as that would not be physically possible (i.e., they have to have it finalized for production runs of the physical retail package).