This is speculation but they could be doing this. If they revamp the class system and say make "onion knight" the base class a player is and then the job crystal changes person to said job then the first trick is what do you do about going from weapon to job when you first get the job in question.

If they indeed do away with classes I feel like they may do the following:
-Onion Knight will be the base "title" for every adventurer
-The weapon the Onion Knight uses will determine the skillset they have available
-When you change to a job and have no weapon in hand you will be bare-handed
-Abilities will have a "required weapon/job" tool-tip attached to them so in the case of changing into a DRK with no greatsword you would not be able to use any of the abilities which require a Great Sword to use

That's my best guess though if they want to make all the current jobs the same however what they could do for the current class/job system is just have it where 50+ they level separately so from 50+ you have to level both SMN and SCH if you want them at 60 and you can't just lv Arcanist to 60 and have both jobs at 60. With that in mind SMN and SCH would learn completely unique abilities from one another from 50-60 and woudl not share anything between one another in that window of lvs. AKA there will be no addition to class abilities rather abilities will only be tied to jobs from 50+ however abilities from 50+ may be cross-classable.