I'm excited to see that jobs have perks now.
It would be safe to assume, I'd think, that many of these perks in place right now are placeholders, until better perks are added.
Tbh, I'm not sure what most of the current "passive" level 30 perks are... and perhaps that should be better explained.

But, it's no secret that some jobs are preferred over others, and some jobs are nearly not used at all.
Adding perks, it's a delicate act of trying to keep the jobs balanced and also try to make them all equally appealing, and also not removing anything from existing donor ranks or custom enchantments. Also, the perks should be relevant to the job they're attached to.
I'm not sure I could do that, but I can offer ideas on what some of the jobs could have.

All jobs suggestions: it would be neat if you could get an improved version of your mcmmo ability if possible.
While the tags come at level 50, perhaps, a "mastertag" for max level could be added... "masterbuilder", "prowoodcutter" or something - just a thought.
Also, custom cosmetics for each job perhaps
Custom crafting recipes could/should utilise "useless" items that are a byproduct of a job
Perhaps any job that uses a tool could learn how to fix or craft their designated tool

Woodcutter - climbs tall trees and chops them down, sometimes falls.
possible perks: ability to climb trees, reduced/negated fall damage.

Miner - mines the bowels of the world, looking for shiny stuffs; finds lava too often
possible perks - reduced fire damage, nightvision

Builder - builds to the sky
possible perks - it has nice perks already, perhaps adding an ability to temporary fly (like 30 min per day), or reducing fall damage

Digger - digs deserts dry
possible perks - not sure, maybe some loot chances from digging, or double smelt chance on glass

Farmer - grows crops and harvests them
possible perks - extra crops harvested, better herbalism skills

Hunter - seeks and kills the monsters of the land
possible perks - chance for mob head drops, ability to track mobs (i.e. /track creeper finds the nearest creepers and tells you what direction, how far) - this last idea would be nice if custom bosses were ever added again

Fisherman - catches things from the sea
possible perks - custom loot from fishing, perhaps an innate "impaling" effect against sea mobs

Blacksmith - crafts armors/weapons and repairs them
possible perks - /fix is a no brainer, although perhaps it should be limited to times/day or cooldown; ability to craft weapons/tools/armor with slightly better than vanilla enchants (thinking like the vote pickaxe) for increased material costs

Brewer - makes the finest potions
possible perks - /stack would be nice for such a profession; dealing with such noxious ingredients could give them a bonus resistance to poison and other negative effects; addition of the actual brewing plugin to tie in would be neat, if possible

Herdsman - breeds and culls animals for a living
possible perks - with farm mob spawners, and a limiting mob cap, breeding/culling isn't very good; perhaps, an increased drop rate of items from those mobs would make them more useful; a tie in to the new horse plugin seems logical, if the herdsman can evaluate horses and breed the best ones

Cook - makes food for a living
possible perks - custom food recipes, some could have bonus effects

This is just a starter list.
I hope more people on the server will chip in with ideas, and perhaps, get the jobs to all have desirable perks.
I'll add more if I think of any, thanks for reading.