Sounds fine Don....
Main concern is not to breal existing code, but I do agree that new stuff should use namespaces (even if it doesn make everything look like a giant PERL script ;)
Is there a migration step we could use for some of this? i.e. create namespace versions of existing stuff whilst keeping the originals.. new installs etc could perhaps choose not to install the orginal stuff... whereas existing systems would still have access to old functions, but also have new ones in parallel... although not ideal it may be a gradual way to convert whilst allowing new systems to use new stuff only...... ?