Vanilla nether portal is broken. the main reason for this is because it has 2 blocks that you can technically use to teleport. the left side can lead to a completely different portal than the right, and it gets ugly from there.
before you know it, you have 20 nether portals in a single chunk and they all lead somewhere else from the nether. you become ghast bait.
so why not have an industrial block similar to the teleporter that can be used to go to the nether? use a different (1 to 1) mechanic to teleport to and from the nether.
this is more a play-ability fix than anything else.
just a piece of obsidian with a chip to craft it.
a button on the block to operate.
still have to build the frame, but each block in the frame takes you somewhere else in the nether, leaving an obsidian block with a button for the return trip.
of course the current teleporter could be reconfigured to be able to go different dimensions and solve the problem that way aswell.