Whilst we don't have a design yet for this, could there be a way to get to the editor to: 

• Show the Jenkinsfile so you can copy it as text when opened from a branch
• Show the copy/paste old expeirence from a known URL with no SCM integration
• Show editable text area when opened from a branch via some url

The last one is to aid contributors/debuggers if there are problems with round trip to declarative, first one is for if github is shitting the bed. 

Middle one is just to keep it around as it can be a handy thing that evolved in playground 

Out of scope: 

• Anything visible that doesn't yet have a design. These are all hidden things to aid supportability.