Just so you know, email traffic suggests a release candidate for Solr/Lucene 5.0 will appear in December, 2014.
If you are curious, see the unreleased Solr Reference Guide (for Solr 5.0).
If you are even more curious, see the issues targeted for Solr 5.0.
OK, I have to admit that not everyone uses Solr so see also the issues targeted for Lucene 5.0.
Nothing like a pre-holiday software drop to provide leisure activities for the holidays!