I actually think you can cleanly separate a lot of it out. When first going to dalaran (evokers likely not having an option to do broken shore), you just get directed to a board or khadgar to progress on to a zone. And if they finish all those or are level 45 (unsure what they start off at) they just get the suramar breadcrumb from khadgar in dalaran to meet thalyssra.
The only story element that would not be clean would be the light’s heart part. That does have clear class hall ties but blizz could just make evokers have the end steps of turning in lead a phased version of paladin order hall (like we did at times during the priest and dk campaigns) to turn in the heart there and for subsequent quest pickups. After they complete the rescue illidan soul’s part they will no longer be able to enter that phased order hall.
Or they could just put a dais for light’s heart somewhere in dalaran for them to use.
The rest of the suramar and insurrection campaigns don’t need artifacts or order hall. And the 7.2 questline unlock just won’t offer the original 36 breadcrumbs leading to mage tower storyline which led into mage tower.
Repeat for 7.3.