I can see them adding weapon classes like "Entertainer" and "Vagrant" like you're suggesting. But I could also see how some of these jobs like Bard, Summoner, etc. could just be added as jobs. I think it just comes down to how much complexity they are going to allow the job system, the more minimalist jobs are (ex. just a title with some passives) the more they'll have to rely on the armory class to introduce new "class mechanics". But if they allow a significant degree of complexity to jobs (their own skill learning system with sufficient number of skills to use) then they could be introduced just as jobs.
With the "Entertainer" solution, the Bard Job is going to have a very strong incentive to use the Entertainer weapon with that job, which makes sense. Packing those skills into the Job system means you can have more incentive to mix the Job with different weapons like having Bard/Pugilist for a melee Bard or Bard/Arcanist for mage Bard.
That's why I hope they post more info about how the job system is going to work because until we see that we can't really figure out what kind of solutions would make more sense.