On a related note, the most principled approach to macros for an infix language I've yet seen is Honu (brought to you by the Racket people): http://www.cs.utah.edu/plt/publications/gpce12-rf.pdf.
Do you know how does it compares with Dylan's macros?
I'm probably going to post about it soon in more detail, if people are interested.
Personally I didn't find myself wanting all of the Racket syntax to be transformed. but I certainly more than once wanted to have a form which would offer infix syntax for everything inside, like TCL's `expr` (IIRC). There's https://github.com/marcomaggi/Infix/blob/master/infix/infix.... but I don't know if it works with Racket. Having a `lang` for infix notation seems like a good alternative: everything that would benefit from it (mainly maths in my case) would be in a separate file anyway.
So you have at least one interested person now :)