This is a bit easier to handle than the pypi transition. The parts of the CPAN ecosystem are more disconnected. MetaCPAN/search.cpan.org (search and docs viewer), PAUSE (upload service), and CPAN (file mirrors) are all separate systems.
Didn't that transition not go very smoothly? I seem to remember having nowhere to download packages stuff at work when they turned the old system off (I think due to the new system not being able to handle the load, but I could be wrong)
There were issues with the CDN and redirects[0] for a couple of hours when they flicked the switch. Still, I think it was a very successful transition.
I've been working a lot more with Ruby the last while and I've noticed links to rubyforge here and there and everywhere but google as I may I can't find where all that stuff has moved to. I think this may be a good counter-example ...
Also, experienced something similar with codehaus.org in the java world a few years ago.
Super thanks to the team for the CPAN search (it was a lifesaver many times for me in the past!) as well as for their awesome transition plan.