Ah... the picture is starting to come together...
Take a look at the "splash" page at Glen's site. Does that room look familiar?
http://www.glenballard.com/
From the looks of things (in the gallery), he and Dave Stewart are, like, BFF's, so it's no coincidence that he is hanging out at Glen's house. So what could the three of them be up to? Could it be that Glen asked them to come over his house to write songs for some other artists that he is currently producing? Could they be working on a Stevie project? Could they be forming a supergroup? Who else is working at Glen's house?
Since Glen is unquestionably a big time hitmaker, whatever they are working on has to be BIG.