Hello and welcome. I think it's great you're being so supportive of your son, though as mentioned by others, it's very important for him to be diapering and changing himself. And being very aware of keeping good hygiene. At that age, if anything kids are absolutely brutal and I'm sure the last thing you'd want would be for him to be bullied for being a stinky kid who still wears diapers. Overall though, it's good he found something harmless that brings him so much joy. Especially at that crucial emotionally turbulent age. Who knows, maybe it's just a phase and he'll grow out of it. Maybe not. Rest assured though, it certainly doesn't mean he won't grow up to be a perfectly functional member of society. My facination with diapers started around age 11 too. Like your son, I'm high functioning and on the spectrum, but still got great grades in school, got a college degree, and recently started working as a scientist.
It's obvious you love and care very much for your son, and he's incredibly lucky to have someone like you there for him. Best wishes