I'm assuming that the migration from 7 to 8 will be roughly just as painful as the migration from XP to 7, ...
That all depends. Some new versions are mainly improved versions of the previous version correcting some of the problems of that previous version, which was the case of the migration from Vista to 7. Other times it's a major departure from the previous version, which was the case going from XP to Vista.
Therefore, the major pain you experienced transitioning from XP to 7 also involved that major transition from XP to Vista. I also made that transition (XP to 7) a few years ago. I still am not as productive in 7 as I am in XP. I have text file archives that I need to search, but Win7's search has been completely screwed up, so I cannot perform those searches. grep no longer works on the command line, so I don't even have that tool anymore. I have just recently discovered the existence of FINDSTR, but haven't had the time to experiment with it yet. And, yes, I have tried some third-party search utilities, all of which were just as bad as the native utility (eg, went to a specific directory, verified the existence of a file in that directory, did a search for that specific file's name, and search could not find it with both hands and a flashlight). WinXP's search is a dream to use and very effective. Win7's "improved" search is a piece of crap. And when I experience networking problems Win7 is a nightmare, whereas XP is a dream to work with.
I have been a software engineer since 1982, working mainly with embedded software. The newer versions do not allow some of our development tools to work. That robs us of the ability to support our products. As a result, we need to maintain older versions of Windows and have to be very creative in finding ways of working around Microsoft.
I was also in the Navy Reserve, now retired. Every time a new version of Windows would come out, the Navy would immediately order that nobody buy until they could test it out thoroughly to determine the detrimental impact of using it. Usually, they'd have to adopt it anyway since our vendors wouldn't supply us with anything but the new version. Private sector companies experience the same problems and the same reluctance to adopt.
What migrating to 8 would involve, I don't know. I only adopt when I have to buy a new computer for home. My main problem with every single version was "Where the hell are they hiding it
this time?" Like being able to change the shell's PATH environment variable. Though now with networking problems in 7 it's trying to find a dialog to do some useful troubleshooting. The only actual improvement I found in Win7 was that the help utility finally became helpful.
That idiotic tiled interface on Win8 is the biggest obstacle for me. Really stupid waste of real estate! I talked with a user and he said it always started up that way and you had to then move to an alternative screen which completely changed how to get to anything useful. Another user was complaining about unexpected changes in how email was being handled, such that an email that he thought had been sent wasn't.
I successfully dodged the Vista bullet and probably will do the same with 8, since the next time I buy a computer I'll have to deal with the "improvements" of 10.