I wouldn't want yet-another-communication-app on my phone and/or browser for a single purpose.  I'd forget it existed and it would become bloatware.

That said, if you can make discourse auto-forward to e-mail, and for discourse to handle responses via e-mail replies, then I doubt I'd tell the difference, right?  In this instances I'd see no reason to spoil other people's fun - they can have their app, and I'll correspond by e-mail?