If it was staying “Classic” forever and there was no TBC in the works they would not be updating things to be better for Arena.
There have been other “TBC” era changes (this was not actually a TBC change), but other changes that are inline with TBC’s combat system that no one seems to have noticed like adding 5 sec to drop combat after an Honor kill, that as I recall was a 2.0 change, and its here now.
Suspected and most logical conclusion, they are prepping the engine for TBC.