You guys all know this is part one of a two part story right?

From what I've been reading the past 8-10 months, they dropped all that. Avengers 3 and 4 will be their own separate movies now. Infinity War may still set up Avengers 4, but they dropped the whole Infinity War Part 1 and 2 stuff. Infinity War and Avengers 4 will pretty much be like Batman Begins and The Dark Knight, or The Dark Knight and The Dark Knight Rises. Sure, the next movie continues the story, but they won't seem like one giant movie split into two parts. It's not going to be like Harry Potter 7 Part 1 and 2 anymore.

I can see Avengers 4 being a soft reboot of the franchise, like a new Avengers thing. Perhaps with a higher female presence.

I'm pretty sure you're wrong. I've heard nothing about there being any sort of followup to this film. From what I've read, this was a standalone adventure, and a way to sort of clear the slate of some of the extra characters before the next Marvel "phase" begins. They plan to introduce some new characters. Highly doubt they will return to the Thanos storyline anytime soon.