On April 1 SQL Server 2016 Release Candidate 2 was released along with the SQL Server Management Studio March 2016 preview refresh v13.0.13000.55. This new version of SSMS uses the Visual Studio 2015 Isolated shell and doesn’t allow any 3rd party extensions like Tabs Studio.
Update (May 10, 2016): Thanks to Karl Burtram from Microsoft, Tabs Studio is now in the SSMS 2016 package load inclusion list.
Tabs Studio Blog (organizing Visual Studio document tabs) 
Redgate SQL promt is allowed.
Comment by Anonymous — April 10, 2016 @ 1:47 am
Can you please show me a screenshot of the new SSMS with SQL Prompt? I’ve installed it, but don’t see it activated.
Comment by Sergey Vlasov — April 10, 2016 @ 6:54 am
I’ve installed SQL Prompt 7.2.0.235 beta (7th April 2016) and now I see it in SSMS. Thanks for the heads up!
Comment by Sergey Vlasov — April 10, 2016 @ 7:07 am
sorry for the late reply. just saw your reply. yes. the beta version installs it and the support blog at redgate mentioned a rapid response to the release, probably due to the fact that existing code for the preview SSM version was incompatible with the RC.
Comment by Anonymous — April 11, 2016 @ 1:04 am
Thanks for the hassle, microsoft.
Comment by Anonymous — April 11, 2016 @ 1:08 am
Any love?
Comment by Anonymous — April 25, 2016 @ 8:30 pm
I asked ([1], [2]) about 3rd party extensions on the SQL Server Release Services blog. No answer so far. As for SQL Prompt – it is white listed in the ssms.exe.
Comment by Sergey Vlasov — April 28, 2016 @ 2:24 pm
Hey Sergey, How did you find out about Sql Prompt being white listed? Is there a way for other products to do that?
Comment by Latish Sehgal — April 30, 2016 @ 5:03 am
Latish,
If I change package GUID for my test SSMS extension to the one used by SQL Prompt {e33b8a3b-d1cf-4eb0-92aa-0590f0b55b1a} then it is successfully loaded in SSMS. You can find this guid in ssms.exe searching for bytes 0590f0b55b1a.
I’m also very interested to find a way to get in this list.
Comment by Sergey Vlasov — April 30, 2016 @ 11:16 pm
I have filed a bug with Microsoft and directed them to tabsstudio. Hopefully it will get some votes and MS will take this seriously. Lost without multiple rows of tabs. Love the other featuers too…
Comment by Richard Tolley — April 30, 2016 @ 10:16 pm
Link to bug @ microsoft https://connect.microsoft.com/SQLServer/feedback/details/2652705
Comment by Richard Tolley — April 30, 2016 @ 10:18 pm
Richard,
Thank you for opening the bug!
I’ve found another relevant suggestion Enable loading of VsPackage extensions in Sql Server Management Studio by Leigh Waldie. It provides a workaround requiring user interaction to load a 3rd party package and it works for my test extension (at least some progress!). On the other hand, Charles Gagnon @ Microsoft says they don’t currently support VsPackage for SSMS and Won’t Fix.
Comment by Sergey Vlasov — April 30, 2016 @ 11:09 pm
Hi Sergey, SSMS is currently using a package load inclusion list to avoid side-by-side issues with Visual Studio 2015. We plan to open up the SSMS extensibility model once we can provide a solid user experience. Please contact me at karlb @ Microsoft to discuss options for loading Tabs Studio in SSMS 2016 RC2+ builds.
Comment by Karl Burtram — May 2, 2016 @ 10:43 pm
Sergey, Karl, THANK YOU 🙂 – Tabs Studio in SSMS 2016 RC3 🙂 Life has returned to normal 🙂 THANK YOU!
Comment by Richard Tolley — May 11, 2016 @ 10:57 am