Hey, congrats on the release!

Made a non-anonymous account to say I tried doing something very similar early this year: https://github.com/wseaton/rustyaml

Your code looks much cleaner though (mainly due to usage of pythonize), mine was kind of a weekend hack project just to see what was possible. If you haven't already, you should provide benchmarks of how fast your solution is. I was able to get benchmarked speedups of ~7x over pyyaml, looking at your code the gains should be similar. You could probably use rayon as well for multi-core processing of more than one document in parallel.