Thanks for your extensive feedback! Sadly, I didn't find the time to test Luna (neither the old, nor the new version) in combination with the new OSMC skin.
I've created an issue on GitHub to track the first error (shouldn't be too hard to resolve).
The second part of the logs you've posted aren't errors. Luna has mDNS support now, but only if the zeroconf package is installed, which needs to be done so using pip. Since I can't enforce this, using mDNS is entirely optional and done automatically - if zeroconf isn't installed, the discovery agent can't be loaded (it fails right on import), which subsequently triggers this log entry as information.
And yes, if the discovery agent can't be loaded or fails to discover any hosts (there's a bug on the current version of zeroconf, which caused some problems), the fallback is always an IP input field. That's a Kodi standard class however, which is supposed to work on every skin.
I'll try to have a look at this soon and see if this also happens on a new addon which just opens this kind of dialog.
Meanwhile, I'd suggest either installing zeroconf and rely on mDNS to discover your host or pair using another skin and just switch back to the new OSMC skin afterwards.