It is already that feature on the forum, I'm checking the settings on my profile to see which button is to enable quick reply.
Edit: Go to Look and Layout Preferences then Use quick reply on topic display: Show, on by default.
Topic: Quick reply boxes (Read 999 times)
I think a quick reply box would be useful on here.
Just for the hack of it?I dont see any convenience. I think the 'reply' button is good option 
I think a quick reply box would be useful on here. Something like this:
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