He is reading at around K level and will definitely be reading more soon. He is passionate about books and about facts.
I agree with knute974 about asking them what they think of his skills. I'd ask specifically about areas where your son differs from Steiner's ideas.
Just wondering: you're a skeptic and you think it's a lot of hogwash. If this is how you feel going in, how will you feel after four months, with six more to go? Steiner's ideas on child development are pretty rigid. I presume that many or most of the people who commit to working at a Waldorf school have faith in the philosophy. Where does his prospective teacher fit in there? How will s/he react to your son and treat him? Is there a risk that he'll spend the year among people who think he's damaged because he can read and do math?
I'm curious about why you think your son won't get into the Montessori school. Are you going to try anyway?
Last question: why is preschool so important? It's not like he's going to get any academic enrichment. So that leaves playing, which he could do at day care. My kids went to a family day care place and still go back because they love it so much (my youngest is 7). It had structure like a preschool.
If you child is already reading, and could handle the idea that school is for playing and he isn't allowed to read there, then I'd give it a try. Schools have lots of strange rules, and we expect kids to follow them (asking permission to use the bathroom?)....
Personally, I don't like the idea of telling my kids to hide the truth about who they are, as I think this sets them up for feeling that they're weird or that being smart is something bad that must be hidden. Asking to go to the bathroom is important for a lot of reasons (e.g. teacher needs to know where you are).
But I'm not advocating for bragging or telling the world how brilliant my kid is, as this can be equally damaging. I guess an example of this extreme would be writing a blog or book about my super-smart child and using his real name and/or photos. That would invade his privacy and set him up for possible stress later (not to mention ridicule from mean kids or parents who happen upon the blog or book or whatever). But I also would never tell my kids to pretend they can't do something when they can, for fear of making them feel like they're weird. I try to take a matter-of-fact approach: this is who I am, this is who my kid is, we're not perfect but this is normal for us, and that's okay.