Intuitively, it seems like the Correct™ feature to handle the concepts of "issues" and "discussions" would be to have only one place to go to comment on a project.

There doesn't seem to be enough of a separation between the concepts of "issues" and "discussions" to support separating them into two features.

Given that discussions seem more general, it seems like the right path forward would be to have only discussions. Sub-features of issues could be added to discussions.