Got my last 4 today. Apparently I was one of the lucky few, the guy at GS said they had 10 preorders for Ike and could only fulfill 3 of them. That's just insane to me.
I feel like Wave 4 is going to take a lot longer to show up the more I think about it.
We're getting a new line on the 20th, there's talk of restocks of Ike, Dedede, Marth, and Shulk. Speculation of restocks of WFT, Villager and Mac- as well as speculation Meta Knight is time exclusive. On top of that, these figures are likely driving sales of Smash, which is getting Mewtwo DLC sometime in late March-May (and could also include more than just Mewtwo).
This would put the newest wave sometime in the summer. If they're assessing production, or wanting to reduce costs by shipping more in bulk which include the restocks, this could lead to Wave 4 launching later rather than sooner. This also would have perfect timing for wave 5/6 launching closer to Christmas in 2 fast batches of 6. They could announce DLC at some point to fill in the gap months where no amiibo are coming out for the game and keep people interested.