If build times are fast enough, it just might be feasible to create a robust compile-as-you-type plugin for your favorite editor, for interactive compile-time error checking. It's the one thing I always liked about using Java IDEs.
Supporting some kind of semantic server that will provide type information and information about comptime computations is one of the goals of the self hosted compiler.
Currently no work has been done on this as the focus is on the incremental linkers and codegen but I personally think we should be able to make a pretty solid tool that will not only provide langserv capabilities but also allow us to inspect and debug metaprograms with ease :)
