I've seen many experienced users, even after months of practise with new systems, in despair because common tasks in their job take 3 or 4 times longer than before.
We've a few machines around here that no one else will touch unless it's either flat impossible to do with software older than Windows 8/Office 2003/etc., or it's the last machine available. I wish it were not the case, but the UI/UX/whatever-damned-marketing-phrase-comes-next breakage in user training/comprehension is beyond being reasonable. Which is why, despite having others play with it as well, Windows 10 is dead-on-arrival. As for myself, a VM and that's as far as it goes so I can at least suss out answers, but this isn't my first, or fifteenth for that matter, desktop upgrade rodeo.
Way back when desktop computing was new, one of the first considerations after collecting what/how/when of (business/technical) processes was presentation to the user. Yes, retraining was going to feature large but the most basic consideration was where the new process fit into their expectations and the (corporate/technical) culture. There's a lot of friction involved in any re-engineering/re-imagining (more marketing speak) of how to do something better (for certain dimensions of better ;-). Early process changes usually involved presentation of business documents on screen so the old interfaced well with the new from the user perspective. Later iterations could/would deviate but in no case was a radical change involved. Frankly, short of firing all the old workers, any change that radical wouldn't be accepted by the users and if forced, well they have feet which they can drag in in using it or, worse, a collective beat feet, unless that was the objective in the first place. I've wondered if in a few cases that wasn't the intent (see outsourcing).
Sure, Microsoft needed to sell upgrades so they could tap that cash flow. Now? Not so much, especially if they get costs down for Support (or have subscription fees, which ain't happening except for Office). I don't think they've adjusted to the new paradigm. Support costs are going to be huge, so where else are they saving costs to justify this 'free' upgrade or what new revenue stream is out there has me scratching my head.