Few people will be in your case, having a level 50 character for a very long time and having not advanced the main story line. A lot of content needs you to have ended the main story line (Praetorium), some trials belong to the main story line in more advanced places, some dungeons too. No Trials roulette, no expert roulette (so the best way to get poetic tomes is lost). There are many reasons to go advancing the story as it goes appearing, most people do it.
Anyway the fact that new jobs require the player to complete the main story up to 2.55 does not seem so important. A new player will have to start from level 1 in one of the classes, level up to 30, etc. It seems unlikely that at level 30 they would change classes whithout knowing the first one yet.
It could have been otherwise, be able to start from level 1 in any class (rogue included), but it will not be like that, it seems.
When the expansion arrives many people will be divided between advancing the story line and leveling their main job or jobs to 60 soon, getting better gear, learning the new actions and adapting their play to them, accessing the new raids etc., and leveling a new job, learning to use it and eventually using it in the new end-game content when they arrive to it.
