Everyones Ideas are so great! I love reading about all the possibilities for the game!
My top 5 choices for EPs are City, Farm, School, Family, Seasons (not necessarily in that order)
With a city EP i'd like to have nightlife/dating incorporated as well as apartments. I think apartments would work really well in TS4! Id love to be able to call on your neighbour to hang out, or live on top of a coffee shop in the city. I hope they add a dating app and bring back turn ons/turn offs! It would be nice to be able to choose a variety of likes in another person, one sim might be very shallow and like certain body types and hair colour while another might not have a preference to that but be very trait oriented.
My Ideal farm EP would include pets (cats, dogs, hamster etc) as well as farm animals (horses, pigs, chickens, goats, cows etc) and include tools for larger gardening/growing larger crops (like green houses, tractors, sprinkler system, some kind of contraption to weed the garden very quickly). It would also be nice to be able to run a pet store or shelter if you also own get to work.
As for School, Id like University/College as well as private schools for kids/teens and night classes for working adults! Frats and Sororities should make a come back, and i think you should be able to hold fund raisers and use the money made toward the house! or throw fund "ragers" (party fundraisers). Clubs and sports would be a good edition to a school EP.
Family would make a good GP I think, adding toddlers at least and the ability to choose the length of a life state. Ive heard of others coming up with the idea of a family reunion as a new party type and I think thats fantastic! I also have thought a lot about the option to create multiple households at once in CAS so that you can create extended families. I guess that is kind of a long shot and I haven't ever heard of anyone else who's had that idea but I would love to be able to make grandparents and aunts/uncles and cousins all at once but have them living in separate houses. If expanding into an EP Id like to see more hobbies, like sewing, restoring cars, knitting, different types of dance, sports etc. But I think that that would make another fantastic GP too.
Last but not least is Seasons, I loved in TS3 when they had holidays and festivals! What a great way to have fun and socialize with other sims! Skating and snow boarding should make a come back as well as swimming on the beach!
I guess I am a realistic player which is why I love EPs that are more like real life!