Can one create a fully functional 3×3 portal? (That's 3×3 on the inside, and 5×5 on the outside)
If you're wondering why I would want to do such a thing, it's purely for aesthetic reasons. I have a room with a wall 3 wide built deep within my base and it would be more trouble than it is worth to resize the room. Hence a 3×3 portal would be perfect.
Best Answer
As of snapshot 13w37a, you can now create portals of any size between 2x3 and 21x21. This is a feature in Minecraft 1.7.