It will be separate from posts. So if it was in your feed it could just show a short blurb.
I think just having the UI combine self-replies into a single post would be great. It has costs, so it's self limiting & shouldn't be abused. Kinda how SMS works.
The UI for writing posts could show you've jumped into another memo so you could try to slim it down if you want. That & simple compression & simple markdown would make it KILLER!