And just to state the obvious, Derpy was factually not ableist. The Last Roundup was written by a mother of a disabled child, and Tabitha (fittingly, IMO) derped by giving her a little-boy voice. The only guilty party here is Jayson Thiessen, who let his PC guard down and laughed at a funny face, and who accepted the word "derp", a word that a razor-thin minority thinks should be a banned as a horrible insult against retarded people, instead of taking the word back and turning it to something delightful, taking advantage of by far it's biggest appearance since it's non-offensive South Park creation. And for that guilt, I'm somewhat worried that a great man like Jayson was fired/quit (since coming upon this terrible thought, I haven't found anything solidly confirming/denying it).
I don't care what people on 4chan do. I learned that a long time ago. I really don't care for the .mov series (although I liked Ren & Stimpy). Ashleigh Ball likes it. Good for her. Good for the .mov series. Different strokes for different folks.
And since there are hints that Derpy scenes were quietly censored in post-TLR episodes, it's safe to say that not only did we lose Derpy, but Amy Keating Rogers or anyone else from MLP is never going to be able to write a good MLP episode dealing with the handicapped. None of us are going to have fun with retards. None of us are going to do anything with them. I'm sure I'll survive without that somehow, but I don't think anyone is better off because of it.
I don't think Jayson quit or got fired...In fact, he just recently ordered a $500 commissioned Rainbow Dash plush. So I think he's still on board, but I suppose you can't take that as a full confirmation.
As for the last few sentences...Crackle says BLARGHL! (and that was post-TLR)