If you need to edit a reply you will see the full post creation style editor popup, just fix your reply and click publish. My opinion is they are streamlining Kinja.
ETAA: The post sharing option uses the old editor. Kinja 1.2 uses the new editor for sharing posts.
UPDATE ONE: Mobile phone editing has finally been upgraded.
UPDATE TWO: The allotted editing time is still fifteen minutes and there is a bug, whenever the time expires trying to republish a comment does not produce an error message.