I think they are limited to 4 by available PCIe lanes since they are thunderbolt ports. It would a a confusing mess if they added more ports but only gave them USB 3.1 capability

They could switch them. It's unlikely that you need thunderbolt at 4 ports at the same time. On the other hand, 4 universally usable ports are already a lot. They might not cater for the long tail. Less than 4, and it's not only the tail you are cutting off.

I think it is to be expected by Apple to remove 2 of those 4 in the next generation, or one afterwards. It's a logical (to them) step towards cable-free computing, which is great and all, but is the only way towards it forcing it through the customers?

iPhones 8, X, XR, XS, 11 and 11 Pro have all supported wireless charging but retain the wired charging capability. I don’t think they are incredibly eager to eliminate ports if they don’t gain something from it (thinness, battery life, space for something else, or water resistance for example).

Well, the refreshed 13-inch already only has two ports.

My 2003 12" PowerBook had 2 x USB-A ports, 1 x FireWire 400 port, and 1 x mini-DVI port.

My 2008 13" MacBook Aluminum Unibody had 2 x USB-A ports, and 1 x mini-DisplayPort.

My 2014 15" MacBook Pro has 2 x USB-A, 2 x mini-DisplayPort-style Thunderbolt ports, and 1 x HDMI.

If you want a massive amount of built-in ports, then a MBP has never been your go-to device ...

And it replaced another model that had two Thunderbolt ports. The higher-end 13" MacBook Pros have four ports.