I'm sorry, I had no idea this was a thing and should have had more empathy. Have you formed a position about what would be the best approach?
My son is on the spectrum, what used to be called Asperger's. He does therapy with an Applied Behavior Analysis certified professional and also a group socialization therapy with half a dozen other kids. The group organizers mentioned they prefer the group to be diverse: not all kids have the same issues, so they can help each other. Other than that, the current wisdom here is that children on the spectrum should go to the same school/classes and participate in external activities as much as any other children, but have professionals helping bridge the necessary gaps (like the socialization group, or pedagogic helpers, or even food allergy managers).
Before being diagnosed, my son took classes which also had some other toddlers on the spectrum, one with Down Syndrome, etc. But it's always a diverse, inclusive group. I'd fight fiercely against any suggestions of restricting his social group to any kind/class of kids.
Of course, if other schools cannot provide him with the assistance he needs, you might not have much choice but to put him in "a kindergarten for autistic children". Ideally, you'd be considering what they offer, what he needs, and what other schools offer. This one might be the best. But IMO that makes you and the social system responsible for finding other venues where he can meet and play with other kids. Maybe if you explain that he will be effectively restricted to socialization with his classmates, it can change their suggestion? Maybe they have something extra to offer people who are in your situation (shouldn't be too uncommon)?
Because it's not just about "being taugh to socialize". He also need to have fun, to learn from example, to get frustrated and improve his abilities to deal with that. He will grow to be his own person, you know your role in this is so important that you cannot just go with the flow. So it's nice that you came to HN to discuss, but we're not adequately educated to offer the help you need. Also discuss with professionals and in parent forums (but beware the crazy ones).
There's a lot of data you can gather to help you choose a position and arguments to defend it at the meeting. Do you know people on the spectrum that went to schools like you mention? And do you know people on the spectrum who went to generalist schools? What do you get from their stories? What are the reasons for Denmark to choose this scheme? Are they focusing on the affected children, or in not inconveniencing the other pupils and their parents? What does the science say about this approach? What are your options for arranging playdates for your kid outside school and family?
I hope you have a good meeting, I kinda have high expectations from the social system in Denmark. Your son deserves going to a place where he can be his best self and grow.