There is no more product development taking place on the SX2K platform. I believe one of the lasdt features added was the Malicious Call trace feature that came along in LW33. As far as I know there also was no certification upgrade training test for LW34.
Nothing factual here, but my own guess is the only reason Mitel hasn't M/D'd the thing entirely is it's the only big TDM switch left in their lineup and they do not yet have anything to 100% replace it with in critical life-safety applications. Remember, the 2K comes in a -48v dc configuration & is about the only thing left that does. That's significant in settings where the phones have "by God got to work!