Generally, I would agree that it's a good idea for anyone contemplating marriage to discuss their expectations about children and other important matters, so as to ensure that their expectations are compatible. If the prospective dad knows he's likely to have an autistic child and plans on spending many happy hours building model trains with the kid, whereas the prospective mom knows nothing about autism and is a social butterfly who wants to enroll the kid in the most popular preschool and have frequent playdates with her friends' children, that probably isn't going to work out very well.
But autism shouldn't be regarded as a defect that a person has an obligation to disclose. Autism is a natural human variation. It's not in the same category as a home seller's duty to tell prospective buyers about a termite infestation or a drainage problem.
To the extent that the autistic husband-to-be in the above scenario feels obligated to discuss autism so that his future wife is not unfairly deprived of the child she expects to have, I would argue that this obligation runs both ways. The prospective wife may not know anything about autism, as such, but she does know that her fiancé is an introverted guy who prefers model trains to socializing. In the interest of fairness, maybe she ought to disclose something like this:
"Honey, before we get married, you need to know that I socialize obsessively. This is a highly heritable neurological condition, and if we have children, they could turn out to be just like me. They'll constantly run in and out of the house with a gaggle of friends, laughing and shrieking. Telephones will be glued to their ears at all times. Their idea of conversation with us will consist mainly of nagging us to drive them to the mall, or the movies, or the roller rink, or wherever their friends happen to be hanging out. Their favorite hobby will be shopping. Would you be able to cope with that?"