Not really, aside from Micro.blog and third-party clients usually defaults to Markdown. For example, if you use the Micro.blog editor and click the button to create a hyperlink, it outputs Markdown instead of HTML. So in a way, you’re going a bit “against the grain” by sticking to HTML only, but it’s not really an issue if you’re using an external text editor anyway.
It’s also worth noting that while you can use any HTML you want on your blog, the Micro.blog timeline only allows a limited set of HTML elements and attributes. Anything else will get stripped out.