good idea. If this feature was added i would purchase DE
I would love to see that listing owners can add a blog. I can see that the blog taxonomy is untouched so its ready to use. Than ofcourse you should add a blog sidebar, blogs in the profile page and blog posts on the homepage. I know this can be done with some plugins but it would be great if this was a standard option.
For me its important that also non-business owners should be able to write a blog post, you might want to take this into consideration.