I would love to see a real estate agent too, as @kwanzaabot described it above. That would be a great interactive career that would allow you to follow and guide your sims' actions at work.
I would also like to see part-time jobs return. I miss the bookstore and grocery store clerk jobs from sims 3, which did not consume much of your sims' day while still providing income.
I wish the handyman could be a playable career too, where your sim could go to other homes to not only repair broken objects, but upgrade them as requested for a higher fee. (I also wish playable sims could request their NPC handyman to upgrade objects for a fee).
Everytime the seasons pack gets released, I always kind of hope for a full blown meteorologist or storm chaser career. Those could be be fun.
Also, still waiting on my military, teacher, and lawyer careers to return.