stuff
The problem with that is what I said a few posts ago about portals that reconnect inside the same plane...
A z-axis is not a significant threat to pathfinding (it certainly will potentially geometrically increase the pathfinding cost, though) because we ultimately still have pathing weights that will make sense - diverting around a wall on the z-axis by climbing stairs to go over that wall, and back down, is fundamentally the same as pathing around it on the x- or y- axis by walking to a doorway to bypass the wall. This is because going up one z-axis level before moving across seveal x- or y-axis spaces moves you just as far as just moving on the x- and y-axis alone, excepting the cost of moving across the z-axis.
Using portals, however, unless you make all portals in all parallel planes have 1-to-1 mapping, so that if Portal A on Dimension 1 is 5 x east, 12 y north, and 3 z above Portal B on Dimension 1, then it means Portal A on Deminsion 2 is 5 x east, 12 y north, and 3 z above Portal B on Dimension 2, then you open massive pathing problems.
What if, as I said before, you have a path where it is a straight line to move from point A to point B on a single dimension, perfectly clear of obstacles. Current pathfinding would almost certainly just draw a beeline towards Point B, no questions asked, because it starts from the assumption that a straight line is the fastest route between two points, and doesn't check for alternatives until the straight line is proven impossible. Then, it starts looking for the smallest diversion it can possibly take to reach the same goal, assuming that the closest thing to a straight line would then be the fastest route.
This doesn't always happen, of course, truly labarynthine forts may force pathing through virtually every tile it can find access to before it can find a valid path, but the assumption that it should start with the best/most likely/fastest case, and then check progressively less good paths is the fundemental way in which pathfinding can be economized, because if it checks the assumed best path first, and finds it, then it doesn't need to search for any more paths.
This, however, goes completely out the window when you introduce portals that can skip you around. Suddenly, the fastest route becomes jumping through hyperspace by walking
away from the destination to reach a nearby portal 10 tiles away from which it can simply walk a few steps in another dimension to find a portal that will drop it 10 tiles away from its destination in the original dimension. Because pathing
away from your destination suddenly becomes a viable means of shortening the route to your destination, the notion that the shortest route is the closest thing to a straight line you can get is no longer true. This means that the fundamental assumption that the quickest thing that looks the most like a straight line will be the best path is no longer true, meaning that in order to optimize travel time, pathing will have to check
every possible path that uses a portal to get to the destination, and compare that path with the straight line route, because straight lines are no longer assumed to be the shortest distance.