I think the order should actually be:
- Develop a new feature, add it to an unreleased version of the compiler
- Ask the users for a review
- Run it across a large library of existing programs to prove that it didn’t break anything
- Let it loose on the users, collect feedback, iterate 2.-4. until satisfied
- Write a standard for the new feature
Probably this is not in conflict with your list, but I made it very explicit.