I always assumed that the decline in Desktops would be non-linear.
Obviously a lot of people that used their home systems for email and browsing primarily have moved to laptops or just use their smartphone now.
But there are quite a few use-cases where you do need the power of a "proper" machine.
I reckon that we are at the point where the current tranche of desktop users are ones that really need them.
As for the increase, I wouldn't rule out the increased excitement by the resurgence of AMD into the mix with their better value, massively increased performance CPUs entering the desktop space, along with a plethora of interesting graphics cards,