Micro.blog is adding ActivityPub federation support and cross-posting to Mastodon https://www.manton.org/2018/11/07/microblog-mastodon.html
Micro.blog + Mastodon

For some time, we have been considering how we could open up compatibility between Micro.blog and Mastodon. Any feature that could be disruptive needs to be approached carefully. In this post I want to talk about how Micro.blog supports Mastodon, why I think it’s useful, and anticipate some questions that we’ll get about this feature. We’re launching 2 major features today: Micro.blog can now cross-post to a Mastodon user account, in the same way we cross-post to Twitter, Facebook, Medium, and LinkedIn.

@Gargron This is very interesting. Sometimes I have a longer post that exceeds Mastodon.sdf's char limit (which is fine as it's long) so I don't want/need another instance with a longer limit.

I thought I might use Diaspora for this and post a link on MAstodon but something that did this automatically, federated with ther microblogs and processes 'comments' (well Mastodon replies - like @rpcutts has set up on this blog)...

@andyc Well, you could use Plume or Write.as if you wanted. @Gargron @rpcutts
@Niquarl @andyc @Gargron I prefer a static site. And write.as looks nice but is hosted. For me, half the fun is getting it working, tinkering, breaking it, repeat.

@rpcutts
Oh I see that. Just think it might be bête to use what I said than Diaspora*.

How did you get mastodon in your comments?
@andyc @Gargron

@Niquarl @andyc some JavaScript that uses the mastodon API that looks up the toot that I shared the post with and pulls in any descendants.
@Niquarl @andyc @Gargron looks like Write.as have just launched the alpha of their self hosted offering. https://writefreely.org
WriteFreely

Minimalist, federated, self-hosted blogging platform.

WriteFreely