Interesting discussion...
I use "transition to" and have never considered the confusion possibilities with transition altitudes, etc. But then I am an AC controller (is this another example of the ever more discipline specific training we get these days - the poor new trainees don't even get a few weeks experiencing tower problems first hand etc.).
Ultimately, ambiguity is bad IMO, and I'm sure everyone elses. I for one will attempt to say something different now. But what?
I also thought the transition/conversion was more likely to happen around FL290.
WW