Perhaps I can weigh in a bit. This post is interesting to me because I want to do something similar when I buy a house.

I think 4 ports per room is great. In my room now I have my computer, 2 NAS and, some additional networked electronics (Console, Smart TV, Apple TV, etc). I have a NAS for my photography which has 2 LAN ports, a NAS for my files which is a third LAN port. And then a fourth for my computer. If OP plans to rent out rooms then having four ports per room could be a really smart idea.

I don't have the luxury of 4 drops in my room, I make do with PoE adapter and a network switch. Since most of the heavy traffic is unlikely to leave my room (such as uploading/downloading photos and videos I've taken for events), I'm okay with that. I personally can't imagine why I'd need four drops in every room but why not?

If I set up a room as an office, I can have four drops for my hardware, I'd probably move my NAS boxes to the rack and upgrade my computer to support dual LAN ports, which would leave me with 2 empty drops in the office. But heck, maybe I'll share the office with my wife? My room can use another four: TV, Console, AppleTV, Spare. Four drops in another room for if I ever rent it out or my future kids follow a similar path. Or maybe if I want to move my office because the room it's in makes a better nursery than the empty room?

tl;dr: I personally find two drops to be limiting. 4 seems more than adequate.