On profile page a link with the games the player currently playing
On profile page of each player there should be a link with the games he/she currently playing.
You can also spectate this games but you should not be able to see through fog of war
AdminFizzer (WarLight Creator, WarLight) commented
My only concern about this is with privacy. Some players don't want all of their games on display.
You could still do it, but make it an optional feature. I would argue it should default to off, too, since new players who have not yet discovered the feature might not be aware that all of their games are public.
If you take it a step further, you could even allow players to pick which games they want to show and which they don't, rather than making it an all or nothing. But if you take it this far, you realize that feature already exists: the favorite games feature that exists today is exactly that.
This would be especially useful to see if a player has continued playing in some other games. If a player is inactive in 10 games at once, he must not be at his computer. If he is inactive in only 1/10 games, he is being intentionally slow and deserves a boot.