Hmm, yeah maybe. I see. 
Do you know if this feature is used often? 
It doesn't seem ideal for the creator since it's extra work during publishing and it's hard to keep up with the discussion in several separated communities. 

 Sorry I don't know, I don't use reddit so much; I know that several communities block them to avoid easy spam.
Btw, crossposting on Reddit is like a repost, so we already have it in its basic form.