It would be very useful being able to see the online or offline status of players in the challenges list.
Often, several players are waiting in the challenges list, who can't be all accepted because of the limited games slots. So, when a slot becomes free, we chose to accept an adversary which is currently online. For that, you have to keep switching between challenges list and players list, checking one by one who is or is not online. T'would be simpler to have the information directly in the challenges list.
Post-Editing: Zut... Just noticed that Progressor made a related suggestion already! I should have posted in his thread. Anyway, note that progressor was rightly suggesting it useful for the outcoming challenges, but I'd personally be more interested to see this information in the incoming list :)