Probably a good move. Using the Last Supper would probably invoke a lot of interpretations depending on who you cast as Jesus, Judas, Mark, Matthew, Luke, and Ringo (He was an Apostle, right?) Which is probably a headache you don't need.

If you were feeling REALLY bold you could select a character (or characters) from all of their VODs, shorts and RTs to make into one giant collage of characters for people to examine to try and figure out who is who (like one's I've seen in the past using the entire Simpsons universe of characters and another using a plethora of robots from PC.) Granted, though, such a thing would, indeed, be quite the undertaking and maybe in some cases a challenge to come up with a character you make identifiable in this style of artwork. Maybe in such a collage using the Blockbuster Riffs wouldn't be entirely necessary aside from using the "essential" ones (like Twilight) as some of them are, arguably, riffs on "good movies" done pretty much to either please fans or just for fun, others not likely to have a notable or distinctive enough character in it to render.
Also, again, it'd be an undertaking considering the volume of Riffs done by the guys, the shorts alone would be a challenge.
It's your project, though, man. Keep up the good work and whatever you settle on, I'm sure, will be great.