The house we're moving out of has the master bedroom downstairs and 2 bedrooms upstairs.
Finn slept in our room until he was 3 months old and then we moved him upstairs. During the hell that is the 4 month sleep regression (TTC folks, don't Google, you don't want to know) I slept in the guest room next to his room. Once I'd had enough of the shenanigans and sleep trained him, I went back downstairs. He's a very good sleeper and even without the monitor I'm pretty sure I could hear him downstairs if he really needed me.
I can't say that I love having the bedrooms on separate floors and the house we're buying is a one story ranch. If we were still house hunting and I fell in love with a house that had the master downstairs, we would buy it.
I don't know if that helps anyone, but I just thought I'd share since we are living in that situation.