Speaking as an ipod user, getting back to the WPS screen is as simple as pressing the "play" button. I could definitely see this request being useful, though. Sometimes I'm searching for a new song while listening to something else, and a song I don't want to hear comes on in mid-search. It would be kinda cool to just be able to press play to pause playback from anywhere without going back to the WPS screen (especially since I usually have "follow playlist" enabled, so going to the WPS to pause said song would then return me to that song's directory).
All of that would require quite a rewrite of rockbox code, I'm assuming, so I don't think it will happen. It's a nice idea, though.