Consider what will happen if a legacy application requires
 one version of a module and a new application needs a new
version. This is more common than you might think - some 
CPAN authors aren't as careful about backwards compatibility as others!

in that case, what about i do: update the module from the central location. and in the legacy app, install the older module in local lib ($Project_Root/lib) and add a use lib '$Project_Root/lib' to make sure it continue use the older module.

back to the krang way, I have looked at Krang many times recently and learned a lot about building large Perl app. Krang includes src of all modules and the krang_build makes it easy to build krang from scratch. the Krang::Platform looks easy enough to adopt to our environment.

but I don't feel like building every modules out of src for every release or rebuilding a module for different app. instead, I would like to compile the module once, all the prerequsite modules and reuse them in other apps (copy the modules to the app's local lib) when approriate.