I'd love to see regular expressions in Arc, but just like my comment on infix notation, I don't think it needs to be part of the core language. A module system is already in the list of candidates and I believe with a good module system, regular expressions could be added to the language by an outside and benevolent hacker or by the core team (i.e., PG and RM) as an included module rather than as part of the Arc language itself. By the same token, I would love to see of the code now (e.g., the app.arc, srv.arc, and html.arc) refactored into modules once the system is complete.
As an aside, both me and raymyers have written basic module systems.
The hardest part (which we haven't built yet) is macros, both private in the module, and macros defined by the module for use by external code/other modules.
