Assumptions like this irritate me. Maud's "symptoms" are incredibly vague and could be attributed to a large number of psychological disorders, if one were to be the cause. She could be showing symptoms of depression for all we know. But, and let's face it, the brony fandom has a very large autistic/asperger portion, and so are undoubtedly biased in labelling character with what they themselves understand.
This is by no means an attack on autism/asperger's. I personally do not care if someone is autistic in the same way that I do not care of someone's sexuality or whathaveyou. However, I feel that many people want a character to relate to, a character they can say "hey, (s)he's just like me!" And thus end up projecting their situations onto characters where there is no evidence.
Character is quiet and introverted? Must be asperger's!
Character has short attention span? You got ADHD, buddy!
Character likes neatness? OCD, here we come!
While these are traits of said disorders, they are by no means exclusive. A quiet, smart person does not equal asperger's. As someone said above, Maud was quite aware of her social situation and standing within the mane 6. She simply said nothing to avoid upsetting Pinkie. Social awareness is key in diagnosing Asperger's. After all, it is on the same spectrum as Autism and the 'aut' in that comes from auto; pertaining to themselves, hence why the whole spectrum is universally defined as having lacking social skills/awareness. This is unrelated to intelligence, before anyone accuses me of calling those with Asperger's stupid, which is not the case.
I suppose it can be an interesting fanon, but it is certainly not serious within the show. If it were, it would be front and centre, as her syndrome would have been the whole reason she wasn't bonding well the with the mane 5. Think Flight to the Finish.