I definitely second this suggestion, though I would prefer the markers appear at the top, just under or above the ruler.
I also generally use the Key Editor in a separate window since there generally isn’t enough vertical space to use it in the project window, especially when dealing with an instrument track that uses a bunch of key switches (e.g. I’m currently working with UJAM’s VG-SPARKLE, which has 3 octaves of key switches in addition to 2.5 octaves of notes). While I can keep a separate markers view window to be able to move to specific places, there isn’t a way to see where I’m at when actually editing in the (full screen) Key Editor.
FWIW, I am primarily using markers for song structure elements, such as start of each verse, chorus, pre-chorus, bridge, etc.