I have a few points to add:
His tweets in November and December of 2014 show an increasing disillusionment with GamerGate - it does make me wonder why someone would then use a play on GamerGate as the basis for their online identity going forward.
These tweets lamenting the direction of GG came exactly around the time
Jim "left" GG. Now, it's not exactly clear when Jim actually put this statement out there, but by the looks of things there are multiple reuploads of this to YouTube from the exact same day - 30/11/2014 - which indicates to me that lots of people got this reuploaded quickly. The original vocaroo recording is gone, and the Internet Archive doesn't have a copy. Either way, I would say this was uploaded on November 29 at the very earliest. We know that when he's not ripping the head off of it to drawings of school girls, or running the Gunts business Empire for him, Gator enjoys dreaming about being Jim - so the fact @ShutUp_Sarcasm has attempted to remain in perfect lockstep with Jim is another coincidence that points towards Shannon.
Another point is Gators recent unwanted intervention with regards to Alice from IP2, in which he recommended creating a completely new online identity. I would say it is highly likely that prior to the Killstream Gator had many online aliases that he would delete and replace from time to time, and but for his association with Ralph he would likely delete his Gator social media profiles - his mass deletion of tweets is a compromise position.
It's still a bit of a stretch that this is Gator, but absolutely believable.