I think we’re going to keep requiring the “http” part of URLs. Micro.blog will auto-link full URLs without requiring the Markdown, but I’ve found with similar features that if I try to make it too clever, it tends to increase the chance of other unrelated problems, and makes documenting the behavior more difficult.
I could see improving the macOS app’s “Format” menu → “Link” command to be smarter about this, though, since it wouldn’t affect anything else in Micro.blog.