There isn't actually ( nor was there ever ) a 3 node requirement for k8s.
Etcd requires 3 boxes for HA, but nothing stops you running a single node etcd.
I personally run single master clusters, because if the master goes down, you lose management as opposed to actual service availability, so mostly I don't care.
Now that there's anything wrong with your preference.
I might be misremembering it, huh! Yeah, it's pretty much the same as Swarm then (any odd number of manager nodes is valid, and if more than a half go down you only lose the management ability and everything else stays up).
Etcd requires 3 boxes for HA, but nothing stops you running a single node etcd.
I personally run single master clusters, because if the master goes down, you lose management as opposed to actual service availability, so mostly I don't care.
Now that there's anything wrong with your preference.