I was confused to see my characters able to see all these quests in the quest list even if I was using none of the classes in my build. So after killing the Velnia Monkey field boss in Tennant’s Garden, I decided to talk to the Retiarius Master to see what the quest was about…
Apparently, any character can now undertake the quest to become an apprentice of the new classes. The master will give you the quest, as before when you wanted to unlock the class for your character, and you can complete it for a title. So my Warlock is now also a novice gladiator… neat 
However, after talking to the master again, you simply get the usual NPC talk and nothing else happens if you’re not of the right class. But the quest entry persists in the quest list…
Since it’s tagged as “repetitive quest (1/15)”, I presume it’s the quest to get the extra accessories/costumes for that class and it totally irrelevent to any character that doesn’t have the class in the build. So it would be nice to split the quest entry into two separate entries: a “blue” quest entry for the old class unlock/title quest (same as all other lower level Master quests) and a “purple” quest entry for the class-specific content that would be available only to characters of that class.