WPCampus released the accessibility audit of Gutenberg that was conducted by Tenon, starting in late 2018. You can read the 34-page Executive Summary. 💦
WPCampus explains, “This report is best understood as a snapshot of the state of the editor in early 2019.” They note that many of the accessibility issues the report documents have been or are currently being dealt with by the WordPress Accessibility Team and Gutenberg contributors. For that reason, Tenon’s report should be read “as a reference document for measuring continuing progress toward accessibility.”
To help improve Gutenberg based on their findings, Tenon opened 90 issues on GitHub. Six have already been closed as of this writing.