Markdown really seems like more sensible target for the "microblogging" than text or HTML. All the formatting you need for even a proper blogpost, readable plaintext, with extensions can even be pretty useful for programming stuff
This is exactly what I’ve been thinking. Either set up an SSG just for tweets or incorporate into another site. Have an RSS feed set up for the tweets collection and then have some automation service like Zapier, IFTTT etc listen to that feed and then post the tweet on your platform of choice. You can be running a Git Based client side CMS like Tina CMS to add new tweets easily if you don’t want to add the markdown files manually. The only thing you don’t get is the ability to interact with anyone on the platforms. There’s probably some bright spark who can figure that part out using web mentions or something similar.