1. Custom domain capable, so our content will be associated with [blog].mystartup.com instead of [blogplatformname].com in search engines.
2. Automated social media integration, blog posts automatically propagated to Twitter, FB, G+, etc.
2a. Corollary: integrated Disqus comments
3. Content network (Medium.com, Tumblr, Wordpress, Svbtle.com)
4. FOSS platform you can either self-host or host via the organization's P/SAAS service (Wordpress, Ghost). Ideal would be self-hosting yet still capable of #3.
5. Own all your content, whether self-hosted or SAAS hosted.
6. Editor that's both techie and non-techie friendly. Aka, Markdown support for techies, WYSIWYG editor for non-techies. Prefer all posts' source stored as Markdown for easy data portability.
7. Bylines for posts - want to publish not just under the company name, but show author names as well
8. SEO-friendly, especially url's
9. Easily theme-able
10. ...?