As responses (the ones I've gotten) seem to be positive, I put in a couple hours of coding.
My end goal is to do away with the fixed "TEXT 1" "TEXT 2" spoiler boxes and make it so you can add and remove spoilerboxes at will, permitting potentially infinite text and/or image and/or overlay combinations. I also want the overlays to be able to be adjusted as to blend mode, and I also want it so that you can personally choose what gets layered in what order. Also the ability to cut off the left/right half of an overlay, so it's only on part of the image. Tall order? Maybe.
But if we really want sig customization, I feel like that's the way to go.
http://talvieno.com/rekt/sigs/create2.php# is the WIP page.
Saving is disabled for the WIP page.
Over the past couple hours I managed to get it so that a basic Overlay panel can be added procedurally on request. The "OVERLAY" spoiler at the bottom is 100% procedural. You can add more by going into the js console and typing:
Eventually I'll have buttons to do that. The important thing is that I actually figured out how to do it, so that's the steepest part of the mountain climbed. I also figured out how to blend things, which is nice. At the moment the blend setting is hardcoded, but I want there to be color dodge, color burn, screen, difference, hue, etc. settings, and hopefully an opacity slider too.