Propellerhead have announced that Reason 9.5 will support VST version 2.4 plugins and will see a full release on May 29th 2017.
Currently Reason 9.5 is available for beta testing if you wish to try it out earlier. Details about joint the beat release program are available online.
As for rack extensions Propellerhead state that they plan for VSTs to exist alongside rack extensions not replace them.
Reason 9.5 is a free update for Reason 9 users and your copy of Reason 9 should auto update around May 29th 2017.
More details online.