Apparently what I was thinking of was in 1.2; nil pointers used to give semi-meaningful (but useless) results when an address was taken of a subfield, like the usual C implementation of `offsetof`.
https://docs.google.com/document/d/14DgGJKGQeBTNJDXo3YxnlSwv...It was before my time so I don't know what the practical impact was, just inherited some code that needed updating a few years ago...
I have used tagless casting a half-dozen times to deal with JSON vagaries; and overlapping methods today almost constantly. Slice conversions to array pointers is too new to say generally but I had one use-case pretty much immediately.