This is a well-known combo that has been tried extensively. See for example this article which was written before WAR was even released:
There’s also the new most popular combo on the block to consider—Karn, the Great Creator + Mycosynth Lattice. If you have both of these in play, your opponent is locked out of playing spells for the rest of the game, since all their permanents are artifacts and they cannot tap any lands to generate mana. The best part is that you don’t even have to play Mycosynth Lattice in your main deck, since Karn can just search for it from the sideboard, so all you’re using up is one sideboard slot. This combo may seem like a meme, but it could also just have competitive applications, especially in decks like Tron that can assemble both pieces in play by turn 3 relatively easily (all you need is Karn on turn 3 and Tron, or Karn + Tron + Tower on turn 4).
Or this one:
One of the reasons Karn's static ability is so strong is that, much like Stony Silence before it, it stops mana abilities. On its own, this hampers the ability of Mox Opal / Darksteel Citadel decks to cast anything under the Great Creator's watchful eye. However, it also has some interesting implications with Mycosynth Lattice.
Mycosynth Lattice turns all of the opposing lands into artifacts, rendering them inert while Karn is on the battlefield. In other words, this prevents your opponent from casting any spells for the rest of the game. Because Lattice is a six-mana card that is utterly blank on its own, this combo would normally have no shot of seeing competitive play. But Karn's Wish ability changes the equation. It gives you access to the combo without any risk of drawing a six-mana paperweight. In addition, it means that you have no need for card selection to help with assembly. Any time you untap with Karn and six mana sources, you will have the ability to prevent your opponent from ever casting another spell.
Do note that the combo only prevents opponents from tapping for mana. Both these authors say opponent is prevented from casting spells, which is almost but not quite the same - opponent can still cast spells that don't cost mana, such as Surgical Extraction and the flashback on Lava Dart, or if they cast something "without paying its mana cost", e.g. via an already in-play Omniscience.