Most notably, Bare Bones has rewritten BBEdit’s preview command to use the current version of WebKit, which results in much less flashing and scrolling when it’s updating. This is a major step forward, as I had given up using BBEdit’s built-in preview feature due to its distracting flashing every time it tried to update my document as I was writing.
There’s also support for Markdown-specific control over rendering, via the Languages settings, and support for numerous Markdown flavors, including CommonMark, classic Markdown, and MultiMarkdown (which is what I use) if it’s installed.
If you write in BBEdit, now would be a great time to try out its Preview command if you haven’t used it in a while. Assuming, that is, you install the most recent BBEdit beta.