I don't know how taxing on the site hardware it would be to do it, or if this has been discussed before, but I think one problem that has always been for certain meme is that you're likely to run into spoilers for something you haven't finished yet on a meme gallery, thus why memes of such spoilers should go on the gallery of the source material (I.e. A JJBA spoiler on the Baton Roue gallery), but then there's people who think the meme itself should go in the meme's image gallery instead, and that's where the problem pretty much lies.
So, how hard would it be to implement an extra feature that say, underneath or next to the spoiler checkbox on a submission form, is a text box that becomes typable once you check "Spoiler?" which allows you to type in what it spoils? Hypothetically, you could get something like this when you roll over the image in a gallery:
Considering I've had close run-ins, such as nearly running into a XC2 spoiler on the Who Killed Hannibal gallery, this could possibly ease things.