Based on what The Sims 4 has released so far, my expectations for a Seasons expansion pack are as low as possible. I don't expect holidays, festivals, etc... especially after the disappointment of Cats & Dogs not even including other small pets (such as birds, hamsters, etc). A Sims 4: Seasons expansion pack will be just that... Seasons and Weather (honestly, that's probably going to be the name of the pack). The only difference in gameplay the developers are going to add is the fact that seasons will change and weather will be added. That's it. Everything else in the pack will just be one new table, a new chair, a new couch, a new bed, some new clothes (mostly for adult female Sims, of course), and one or two hairstyles that are simply a copy of one that we already have in the game. This seems to be the pattern with The Sims 4. Also, let's not forget that even Sims 3 didn't introduce a new world for Seasons, so do you honestly think Sims 4 would end up adding one? LOL
Also, as for seasons not happening in Oasis Springs, I disagree... honestly, the player should be allowed to choose which seasons and kinds of weather occur in each world of their game. After all, The Sims 4 is supposed to be about "You Rule"... then again, my previous paragraph kind of already explains how that slogan isn't even legit. But regardless... I think they should just give us all the option to choose which seasons and weather will occur in each world per save file. That way we can all play the way we want.