Well... thanks for your answers...
hmmm... of course, a kind of systray and lsxcommand is the strict minimum a theme should offer... but I don't really want to know what kind of module should be there...
I just want to know what feature should be :)

I mean things like (IMO) easy theme management (via !popuptheme), easy wallpaper management, easy window's alpha management... and, oh, thanks gyorka, easy popup entries management. Things like that (that's all my poor imagination let me think about - that's why I'm asking you)