I wouldn't be at all surprised if EOL for Win9 was reduced to 8 years from the current 10, to further boost adoption speeds. Business will not go for an OS that has to be replaced before most of their machines have been upgraded, so will be encouraged to adopt earlier and more often, if it can be sown that the systems are stable enough.
Business manpower churn is such that retraining is needed anyhow - even if many businesses ignore the fact in the hopes of a trickle-down effect from new users and home users.
The only people who specifically and regularly got training in any of the companies that I worked for were the IT staff themselves. Otherwise if you were lucky, you got a 1/2 day intro course (or maybe an hour's one-one training) when the company introduced new software - but never anything for a new OS, as by that time it was considered old hat, and everyone was supposed to know it anyhow. If you had a decent manager, you could ask for training - and if you had a specific project, you could expect it - but otherwise it was mostly on the Simon-says principle and much time was wasted.
Much of the time, a company's unwillingness to upgrade the OS is because of a critical piece of third-party software, which was expected to work in the new OS - but didn't. This was particularly bad on the change from XP to Vista because of the new paradigms which Vista introduced. Those hurdles have now been largely overcome either by updates, or by moving to new systems completely.
There have been no paradigm-shifts involved since Vista - and I haven't heard of any for Win9. Yes, Win 8 went to a touch-centric interface (badly IMHO) but the background was still Vista with bells on.
What Win9 is going to be like I have no idea yet - but I expect that it may be something like the change from Win2K to XP. A much slicker interface but not a lot of really new stuff. MS has still to deliver on a couple of the promises it made in the Alpha stages of Vista, but they'll want to let the dust settle over the bones of Win8 before delivering anything spectacularly different - which may come with Win 10.
At this point in their move to the BYOD generation, MS will want to consolidate their base, and convert more people to subscription services, rather than anything else - so expect the continuation of that trend to come in the apps and Office 365 areas, rather than in the base OS.
The day of the hobbyist PC user is clearly nearing evening - the days of the device user (complete with bruised thumbs) is approaching noon. The business Desktop machine is slowly being replaced either by laptops or by devices, which may get taken home, while the ones who actually probably need desktops (designers and such) may well soon be working remotely from thin clients anyhow.
