The unnoffical Babel 6 Babel 5 style legacy decorator plugin has a slightly different implementation of that actual Babel 5 decorator implementation.
What decorator support does Babel 5 and Babel 6 have?
...the intention is still for Babel 6 to implement the new proposal once it has been officially presented to TC39.
-source: loganfsmyth on Phabricator
So Babel 5 supported the old decorator spec, Babel 6 will support the new decorator spec - when the new spec is settled.
Which begs the question:
When will the new spec be settled and (supported by Babel 6)?
Answer: ...when wycats feels the proposal is ready
-source: logalfsmyth on Phabricator question/answer
References