As far as I'm aware, the Accessibility Team has not been working with the Theme Review Team on this. This has been the Accessibility Team holding meetings on their side of things about the possibility of bringing this up. This is not something we've discussed in our theme review meetings, unless I missed something.

I did want to share some of my concerns. One of my biggest concerns is forcing theme authors to do stuff that core WordPress itself doesn't do. For example, the "read more" tag default output doesn't conform to the accessibility guidelines. This is something that should probably be addressed in core rather than as part of theme review.

My next concern is the even higher barrier to entry for new theme authors. Suppose you're a new theme author who just coded his first drop-down menu. This is like the most awesome thing in the world to you. Suddenly, someone tells you that the drop-downs can't be opened via keyboard and you must recode this. While one is better coded, it doesn't mean the original is incorrect. If someone had told me this the first time I submitted a theme, I would've went elsewhere. Any requirement that unnecessarily hinders new theme authors is not OK in my book.

I mentioned this in my comment, but my other concern is hindering someone's artistic vision. The color contrast guidelines could very well do this. Sometimes, people just want to design something for the sake of designing it. When TRT starts getting into policing a stylistic theme author decision, we're going a bit too far. I'd also argue the same thing about sliders that auto-start (even though I hate sliders).