It seems like it must be much more limited these days. Display transport is packetized, often encrypted (HDCP), and designed to be capable of exceedingly high bandwidths. Versus a CRT that comparatively blasted out a nice sequential analog signal for anyone to listen in on.

That said, if you're using a wireless keyboard it's pretty much a given that the keystrokes can be recovered by timing analysis regardless of the manner of wireless connection. At least unless you happen to hunt and peck painfully slowly.