A centralized module index will be nice, i tend to end up searching github.com which leaves out all the other sites or locations that could have a module that solves my problem.
Note that there's a difference between "central registry" and "central index". In particular, I don't see any downsides from what they are changing - godoc.org is already, for all intents and purposes, a central index, so I don't see how anything changes in that regard.