Just thought of listing new features which you can think for pqa....
1. hidden category. Only allowed people should be able to access this. may be like expert and above should discuss some strategies for qa. etc or ability to add selected users
2. Custom user title. admin should be able to give custom user title, like developer, testing expert etc or teacher, math expert, science expert etc.
3. Poll plugin
4. Survey plugin
5. badges plugin
6. quiz plugin
7. Redesign user profile page.may be like quora or stackoverflow
8. FAQ tab, mark some questions as faq then show those in faq tab.
9. Warn before posting if user post contains restricted words, admin should be able to add restricted words in a list.
10. Forms plugin, check https://ninjaforms.com/
, you can add subscribe by email form, show message form, contact form etc you can add more forms later.
11. blog plugin, give user point if they post something interesting..... for every post like you can give user one point.
12. find duplicate posts, admin feature
13. Accept users only based on invitations from other users of qa. admin can open qa registration for some time then restrict.
14. redesign wall, show twitter kind of messages.
15. social share question.