Cool looking Karn list! I think if you are playing Astrolabe (and it doesn't get banned eventually...) then the 2nd color is basically 'free'. Also, don't forget
Liquimetal Coating in your Karn-board!
I think I am missing a key ingredient in my list, something that makes Ghost Quarter better than Rishadan Port:
Ashiok, Dream Render. I think this is going to be very, very good at denying fetchland activations and controlling top-decks. I think before even the 5th mill-rock there needs to be 2-3 copies of this card. It means I want Dark Ritual again, which is fine because I'm thinking this will only be a 20-22 land deck. I'll start with 1 copy and go from there.
Ashiok I think will be pretty good at gluing a couple of these synergies together.