I hope the next pack has a theme we never had before. Nearly all the eps we've gotten weren't anything new. Get to Work was an equivalent of Ambitions (with less and buggier content ;) ), City Living is similar to Late Night, so is Get Together. And now that we have pets, I would love some more exiting content. I would personally like a Time Travel pack, maybe with the option to travel to the past AND the future.
I am indifferent about Seasons though. On one hand, it would be a great addition to the game, but I am afraid that it wouldn't include toggles to disable certain weather effects/seasons in some worlds (You know Sims 4 doesn't have it this much with toggles, and snow in Oasis Springs would be a deal breaker for me ;( ) I don't even think that Seasons in an ep would be worth it. What could be added besides weather? The seasons ep for TS3 always seemed a bit lackluster for me, so maybe it would be better suited for a gp instead, but that's just my opinion about that.