Does anyone think the whole "Part 1 and Part 2" thing for last in the series movies is going to become normal?

It will become the norm, but only when it's a major series they can milk for more money. Harry Potter I can understand. That'd be a LOT to try to do in one movie, and in the end huge elements would need to be cut. Turning it into two parts was the right move, and was ultimately done for the right reasons (I remember when that decision was made). Plus, they put serious effort into making sure both parts were fully fleshed out and the extra time was used to develop the story more and include more important elements, with plenty happening in both movies. The source material more than provided enough story for two movies.

The final Twilight book, on the other hand, could have easily been done in one film, but that would cut the profits to be made in half. Yet, not nearly enough happened in Part 1 to justify it being its own separate movie. They just endlessly dragged out two or three elements of the book to fill up the time. That alone tells you it was them being greedy.

Mockingjay I'm a bit torn on. I think it could be done quite easily in one movie, but there could maybe be enough there to fully flesh out two movies as well without repeating the Twilight experience. I kinda doubt it though. They'll probably need to stretch some stuff out or add in some extra ideas like they did with the first movie. It'll be quite a bit better done than Breaking Dawn though, I don't doubt. In any case, it doesn't matter. Studios won't settle for the revenues of one film when they can stretch the material into two movies and make double. They'd likely do the same for ALL films in such series, if they thought for one second they could get away with it. People are more tolerant when it's the final installment being split. I think it has something to do with stretching out the experience a bit more right when everyone is sad it's ending soon.

I kinda think Harry Potter unintentionally started this whole thing, even though it was done correctly and for all the right reasons in that case. All the studios kind of had a revelation into how they could get more money out of their series, including those involved in HP in the first place, in the end.

I really hope not. It's starting to get annoying. Why does Mockingjay need two parts? The book is 390 pages long with plenty of repetitive action sequences. They could easily fit it into one movie.

I think it can be a variety of reasons why filmmakers do it. In some cases it's because the source material is *really* long and they need more time to tell the story. But, I think a lot of it (if not most) is money.