Is there a way to identify which RealTracks are "playable" other than going into the editor and seeing if the button is available? Anything in the RealTracks picker, etc. - or a guide online even?

Not at the moment.
You will see the built-in simple player plugin on the Plugin tab for that track.

In build 908 you can type "playable" into the search filter in the RealTracks filter.