I would suggest an additional class of "Open": "Open (Own Platform only)". Obviously, if you're playing on PC, XBox or PS4, you'll see only CMDRs playing whichever platform you're playing upon, and none of the others. In effect, it's just what we have now. To clarify, you'll only see players who are also playing in "Open (Own Platform only)".
However, with full cross-platform play, "Open" becomes "You'll see players playing on any supported platform". It will be true cross-platform play, not the "Open (Own Platform only)" play we currently have where only the background sim is common to all platforms.