The Accessibility Inspector's auditing tool should warn about inconsistent heading level structure.

According to W3C, h1 through h6 elements should be organized consistently. The rules, roughly paraphrased, are:

1. Only one H1 should be present on a page, and it should be the main heading or repeat the page title.
2. Heading levels should not be skipped upwards, one should not go from a h2 to a h4.
3. Downwards skipping is OK since nested sections can lead to that.
4. Only exception is if the heading is moved out of the visible view port, for example when the now considered outdated technique of invisible page section headings is used.

This is something that is definitely part of the original roadmap. I think it should be one of the higher priority items once fission work is finished.