Personally i dont think SE will Limit us to 1 class one job, for the simple fact that Yoshida is rehauling each class for class unequness. Classes are going to have roles in combat already, jobs will just be that additional push.
i think its a good idea to let jobs use any class, or at least DOW jobs only use DOW classes and DOM jobs only use DOM classes, also there will be hybrids that can use both like RDM.. The battle system will be very enjoyable like this cause players can switch out weapons for given situations, like if we have to use piercing, or blunt etc..
The issue on who is getting BLM or WHM between THM and CON will be solved. THM and CON will be effective at BLM since equiping the black mage job grants you high tier blm abilities, which on the other hand the equiped class acts kind of like a sub job..
Also the current thinking is to not have the JOBS use cross class abilities, only enable the abilities from the class equipped. If you have a class equipped as your main, you would be able to equip cross class abilities...
there is your balance people
oh and as for RDM/LNC .... so what..... they will still be effective, the pole will act like a stave with a point on it lol..
at the end of the day Jobs should act like your Main, and Classes should act as your sub...
P.S. SE if you know whats best for the life of XIV and your fans Please dont lock jobs to one class, especially since your trying to fix what tanaka messed up, this decision would be worse than any decision tanaka has made..