Is that really "the simplest things"? :-p It seems to me Arc goes out of its way to avoid interleaving source location information on s-expressions the way Racket does. Putting it back, without substantially changing the way Arc macros are written, seems to me like it would be pretty complicated, and that complication would exist whether Arc was implemented in Racket or not.
Surprisingly it's possible to get pretty close. The trick is to read-syntax rather than read, and then have ac map over syntax objects properly. At that point it's a matter of using eval-syntax rather than eval.
The takeaway is that the error messages are much, much nicer. I'm talking "the error is at line 213 of app.arc in function init-userinfo" nicer.
It's not perfect. And to get to perfect, you'd have to do as you say and rework how macros behave. But it's maybe 90% of the benefit with little work.
