Currently, none of the arguments to AC_INIT can be computed when you run 'configure'.  If you use two-argument AM_INIT_AUTOMAKE, on the other hand, you can pass shell variables as the arguments.  The Automake manual calls this out as a reason to continue using two-argument AM_INIT_AUTOMAKE:

> differently from what happens for AC_INIT invocations, this AM_INIT_AUTOMAKE invocation supports shell variables’ expansions in the PACKAGE and VERSION arguments (which otherwise defaults, respectively, to the PACKAGE_TARNAME and PACKAGE_VERSION defined via the AC_INIT invocation; see The AC_INIT macro in The Autoconf Manual); and this can still be useful in some selected situations. Our hope is that future Autoconf versions will improve their support for package versions defined dynamically at configure runtime; when (and if) this happens, support for the two-args AM_INIT_AUTOMAKE invocation will likely be removed from Automake.

So we should find a way to support shell variable expansion in the arguments to AC_INIT.