We've been wanting to do this for quite some time now... I think, now that Solr/Lucene are merged, and we're looking at opening an unstable line of development for Solr/Lucene, now is the right time to do it.
A standalone module for all analyzers also empowers apps to separately version the analyzers from which version of Solr/Lucene they use, possibly enabling us to remove Version entirely from the analyzers.
We should also do
LUCENE-2309 (decouple, as much as possible, indexer from the analysis API), but I don't think that issue needs to block this consolidation.
Once we do this, there is one place where our users can find all the analyzers that Solr/Lucene provide.