I do not think the entire Season pack should be base game, but I do think seasonal changes for each world should be base game in TS5. I also doubt they will ever make seasonal changes for TS4 base game. It's the main seller for the pack, the only other thing (besides CAS and BB) would be adding holidays and then seasons would be merely a game pack. I personally don't mind if seasonal changes become a base game feature, but I just doubt it will happen.
As for the rest, I don't think any of those really need to be base game. It is a sandbox game where people can add what they want and those are not necessarily features that are needed by everyone. Perhaps some features of parenthood would be nice - but I can also see why it doesn't make sense for everybody. Also, bust the dust, I still don't understand why people wanted this pack in the first place, so I'm definitely going for a no there. Same with pets. I like pets in real life, but I don't want them in my sims game. They're unplayable and just add extra tasks. It's unfortunately not worth it - at least for me.
I do for example think that part of the household dynamics would have made sense to add in the base game, but I can also see why they didnt do it.
I do think newspaper, magazines and landlines would have been nice, just because it's what we had in past games. But then again I can live without.
Realizing, I should have picked other because what I do think should become available and then be basegame is an Online Marketspace, where people can sell their own things like paintings or crafted objects. It fits into our times and you could have a ranking system for it. I'd love the idea.