Thanks!
My goal with this setting is to take the "default" settings and make them coherent while keeping as much of the content as possible. I'm going for the holy grail here--the kitchen sink that's internally consistent while still being recognizably "D&D".
But I've always hated the rigid dragons. And my slight OCD-ness about symmetry makes the presence of poison dragons just feel...off.
I have a more mechanical write-up (a "general" stat block for each age category with placeholders for traits and then instructions on strengthening or weakening them) based on the actual printed stat blocks, but that's for a different forum.