Also, bear in mind that "this person" is not just any Joe Blow but Bozhidar Batsov, maintainer of Rubocop and (as an author of the Ruby Style Guide) something of an authority in the Ruby community.
What's the big difference between x and @1? y and @2? It doesn't really feel that significant to me.
I'm a bit meh on the feature. I'm suspicious of lambdas / blocks that take more than three parameters, and for three parameters I'm good with |x, y, z| or |a, b, c|. I do think that giving them meaningful names is usually obscures intent more than it clarifies; |k, v| for maps and |i| for loops self-document well enough.
Those are massive improvements over "@1 @2".
You make the case yourself. Using "k, v" as a convention immediately signifies these are a key and its value. Using x, y indicate this is a pair (and x and y are of the same type, I assume?).
No more stuttering in single-line blocks.