Create a new repository at hbase.apache.org and commit the new kafka proxy here (
HBASE-15320). Make sure it plays nicely with hbase core making use of public-apis only (It does as best as I can see... but saying this anyways).
Once the kafka proxy is working, as subissue, move REST and thrift over... SPARK too.
This might be better done for an hbase3 target. I filed it against hbase2.2 for now.