It was always my idea, but I wanted to wait to have something a bit usable. I have been using this Micropub composer reliably for a couple of months and seems to be working fine.
It is not a fully compliant client though as it doesn't do HTTP headers link discovery, only through HTML at the moment. Also, it only supports form-encoded syntax for posts.
It's been my first time learning a bunch of new JS tools and syntax, so there's definitely room for improvement. I don't have grander plans for it, but a few items on a checklist to add features.