We should allow gobject-introspection to optionally *enforce* writing in the GObject/C subset that it supports.  A commandline argument such as --fail-unbindable would allow C authors to catch new unbindable functions during development, rather than having us yell at them later.

So this would be a new option to the scanner which C library authors could add if they desired[1].  However we do need an escape hatch for legacy API and C convenience glue.  One way to do this would be a new annotation:

<nointrospect>

or the like which would direct the scanner to ignore it.

[1] I would push for GNOME to try to get all module authors to agree on this by default.