I made a post on something similar to this earlier, but in terms of X-class skills going to the wayside I think something like this could occur with our current jobs:

It's not about removing, it's about phasing them out so that the current structure remains. Like imagine if SE gave lancer a new skill to replace invigorate, replaced pld's provoke, and thm a new skill to replace swift cast. Then they gave each DoW invigorate, Tanks Provoke, and DoM swift cast. Later on we get a replacement job crystal that completely remove all the cross class abilities and grants us more job skills, more of our main stat/vit, and possibly bonus traits. See where this is going?