I prefer 'aikidoist' to 'aikidoka', and I see what you're getting at with "Sensei x" as against "x sensei", though I still don't like it.
"Sempai X" though, is a whole different ball game. "Sempai" is not an honorific, it isn't rank related, it doesn't necessarily have anything to do with teaching, and the vast majority of us practicing in the west don't do the sempai/kohai thing or even understand it.
The way dojos in the UK use "sempai" as a title, meaning "almost, but not quite, sensei" is just plain tacky. Tacky and embarassing. So there.