From a developers perspective I agree it makes sense to put the templates into /packages/acs-subsite/lib. But I still would put them unter /lib/templates or /templates, as this is a more obvious place for the occasional developer to look into. Any package that starts with acs- and looks like core is off limits to the occasional person installing the system (I'd assume) as this is a core package and you don't fuzz with core packages (at least, that's how I behave e.g. with PHP Horde).
OTOH, it is now documented, so if someone searches for the Community Template, this thread can be found ;).