Re: I miss the old days
We used to be able to work out how big the changes were from the numbers
That may work OK for an app. It won't work for a general-purpose operating system. The thing that is most likely to be immediately visible to a non-technical user is a change in the user API causing existing programs to break (which is something that Linux tries very, very hard to avoid). The next most likely is a new bug in a facility that you are using, but that's hardly something that they wanted to ship!
Apart from this, who decides what is a big change? A complete re-working of the code for massively parallel SMP systems may be scarcely visible to a person with a single 4-core CPU (and even less visible to someone working with a single-core embedded peabrain). A new filesystem ( for example Btrfs) may be of huge interest to some, and of no relevance whatsoever to others that aren't intending to use it. And so on.
The switch from Linux 2.x to Linux 3.x was supposedly arbitrary, but did in fact coincide with a major architectural change that the kernel debelopers had been working towards for the best part of a decade. What do you mean, you didn't notice the final demise of the Big Kernel Lock? Well, actually, you weren't supposed to. Its removal was a success. Cause for celebration by kernel developers (and maybe, the reason for the big version number change), but a big yawn for everyone else.
So, is there any reason for Linux kernel going from 3.x to 4.0 other than (maybe) the next release after 3.99? Well, just maybe ...
1.x ... a developer / enthusiast system
2.x ... production-ready, large scale SMP handicapped by big Kernel lock
3.x ... big Kernel lock finally gone, scales from embedded peabrains up to huge datacenters.
What next? I'm hoping for
4.x ... Microsoft abandons its own OS kernel, adopts Linux.