I think your being very short sighted if im honest, most of the PvE systems are already in place since blizzard are happy with the raiding format of LFR/Normal/Heroic/Mythic. With mythic being 20 man for a long while now Blizzard are happy with that for encounter design and does require change. M+ has been a huge success and again doesn't require change only refinement.
Now Blizzard are introducing Warfronts which is a PvE mode in the game.
There is PvP changes with Battlegrounds been taken away and new ones added etc but nothing major.
The point is theres nothing major going on in this expansion as most of the systems are being refined with exceptions of a few things like Warfronts. This is neither a PVE or PVP expansion, its more of a extension to existent systems in place. Ive played like yourself right from vanilla and a expansion doesnt have to have a complete redesign to make a expansion, a expansion is just new story new content to explore etc.
Obviously with a expansion comes changes to classes etc but thats always a ongoing process.
The only thing im disappointed with for the expansion is that its Battle for Azeroth not Battle of 6 islands. I think blizzard are massively under utilising the existing continents of Azeroth and massive opportunity wasted, keeping the content mainly to the 6 islands.