I'd like to resurrect an old idea I had once / flog a dead horse: https://nerd.nu/forums/topic/682-pve-a-thought-question-on-portals-and-their-number/
My idea was, in a nutshell: one portal. Only one. Plonk it down somewhere on the map and - I think - there would be some very interesting knock-on effects in terms of overworld infrastructure development, resource gathering, trade, and so on.
I've always thought that P's infrastructure engineering is one of the best things about the server: I love the occasional "world border to world border" run along the roads; and experts would probably infer weird freakish things about our collective mind from how our rail networks grow. The nether's speedy travel is, I think, it's great attraction but I'm curious to see what would happen when that wasn't available.
(The original post, whose link I've provided above, had some good perspectives on this).