OK, I think I understand now.
That commit 39f65b1 also removed the syntax for as, which as far as I can tell is not documented as part of the old syntax for givens.
I guess it should be called old old syntax then, rather than new new. 
So it seems we have just one new syntax for givens after all, with a nifty type constructor augmentation. Phew.
@som-snytt Your call to arms is noble, but my response must be (cue Northern England accent):
“I can’t be asked.”.