While I find myth interesting, I don't think it should be a 4x at all, maybe 2x. It's a good T1 drop, but you don't want to draw the second. And playing landstill you usually have plenty of time to win, the most important thing is to survive.
Disagree for a few reasons:
1.
So much counter magic hits MR. Even if you're casting it turn one on the play, the average blue deck is going to have
eight main deck counters they can use!
2. In addition to the usual removal like Bolt and Decay, MR is hit by a lot of splash damage from people running cards to destroy Oath, sometimes even in the main deck. This means that backup threats are more necessary.
3. Multiples allow for some really explosive starts, especially when you use one to trigger the other. I've finished the game on turn three by laying multiple MR's on turn 1.
I've been playing MythStill on and off on MTGO and I played a couple rounds with it at GenCon. I know Nedleeds played with it a bit, including having a picture on the Mothership.
For record, on number 3, my most explosive start thus far has been:
Plains -> Myth Realized. Pearl (trigger) -> Myth Realized (trigger). Lotus (trigger trigger) => Ancestral Recall (trigger trigger) => Time Walk (trigger trigger)
This leaves me with 3 cards in hand, an MR with 5 counters and an MR with 3 counters as well as the mana to start using them all before my opponent can take a turn. Obviously, this is a magical christmas land scenario but it's an example