I've read the replies today from Jens, Jonathan, Ville and Jason.
Here's my reply to all of them:

This whole 'interface' thing seemed like such a cool feature when I
thought up of it, that I thought other people would see all the
possibilities it brings too. I've already described how you would
define an interface and how it would work, but now I'm going to do
three things:
(1) Try to come up with approximately 5 good code examples where my
'interface' idea would be very useful and produce very clean and
manageable code.
(2) For each of my approx. 5 examples, I'll write it how it would be
written in C++23, so you can compare and contrast and see if it's
worth changing the core language.
(3) After 1 and 2, I'll get into the nitty gritty of the 'object
model' and show how I would alter/amend certain paragraphs in the
Standard.

If you still think it's a lousy idea after all of that then fair
enough I'll drop it. It will take me a week or two or three to do all
of this and share the 3rd draft of my paper.

Enjoy your weekend.