MBS-4536 is shipped (or, well, will be on production in another two days), picard should probably take advantage of it! The things it can determine from the plain release request (rather than needing to hit the CAA as well) are:
a.) whether there's anything in the CAA for that release at all
b.) how many images are in the CAA
c.) if there's a front image
d.) if there's a back image
I suspect that a.) will be the most useful, since it'll kill off an HTTP request for anything that doesn't have CAA cover art.