Support Registry without any Extras

• SystemJS Version:
• Which library are you using?
  • system.js
  • s.js
  • system-node.cjs
• Which extras are you using?
  • AMD extra
  • Named Exports
  • Named Register
  • Transform
  • [] Use Default
  • Global
  • Dynamic Import Maps
• Are you using any custom hooks?

Question

To resolve an intermittent issue that appears to be tied to the global extra included by system.js, we have switched to using s.js but would like to layer on registry features.

Registry is not distributed as an separate module, is there appetite to support a PR, refactoring registry as an extra?