I've tried just copying the Coda1 plugin to Coda2 but it doesn't seem to work.
According to the panic folks, you usually just need to open the plugin in their plugin creator and re-save it. I did this, and thought it was working -- the menu shows up, the shortcut works, it pops open the peepopen window...but when you hit enter on an item, it closes the peepopen window and does nothing. :(
Would be great if someone could look into this -- seems like there hasn't been an update in ages.
Victory! After looking at the custom url scheme documentation, I figured moving the Coda 2.app folder to Coda.app might work...it does!
(sudo) mv /Applications/Coda\ 2.app /Applications/Coda.app
Note -- before I opened this issue, I had tried symlinking Coda.app to Coda\ 2.app -- that will not do the trick.
Wasn't able to get it to open by re-saving in plugin creator.