I haven't seen any reports of the Armory system being "scrapped", only built upon. Classes are mostly for soloing, and Jobs geared for more strategic party play with defined roles.
If I had to guess, I'd would guess that conjurer would open the "Whitemage" job, but they also said that you may need combinations of different classes to open some jobs. "Blackmage" may very well end up being where you have to have a level x conjurer and a level x thm, so if that is the case you aren't "losing" any progress even. It also may be that thm ends up opening black mage in which case you just have more spells to work with while leveling thm right? Worst case, you won't really lose anything except your assumption that something would lead into something that it didn't. People are crying over spilled milk when the container hasn't even been opened or taken off the shelf yet.
Main point though is that until they say exactly what is what, there is no use getting upset over speculations nor doing that heavy of planning. Its all open to change, we aren't playing a finished product and we shouldn't act like we are.
