Actually I was wrong about the Tempest not being announced at a NAMM show. In fact, it was always announced at Winter NAMM shows in all of its three different incarnations.
To the best of my knowledge, this is an overview over the DSI release history since 2002:
Spring 2002: Announcement of the Evolver; October 29: shipping announcement; first presented at Winter NAMM 2003
December 6, 2003: Announcement of the Poly Evolver Rack, first presented at Winter NAMM 2004; May 10, 2004: shipping announcement
December 23/24, 2004: Announcement of the Poly Evolver Keyboard, first presented at Winter NAMM 2005; May 10, 2005: shipping announcement
January 11, 2006: Announcement of the Mono Evolver Keyboard, first presented at Winter NAMM 2006; May 1: shipping announcement
NAMM 2007: First announcement of what would become the Tempest, here under the name BoomChik
August 20, 2007: Announcement of the Prophet ’08 and the Prophet ’08 Special Edition
August 31, 2007: Shipping announcement for the Prophet ’08 Special Edition (300 limited units)
September 10, 2007: Announcement that Prophet ’08s are shipping in greater numbers
Winter NAMM 2008: Showing prototypes of the LinnDrum II Analog (formerly known as BoomChick; 2nd step in the Tempest development) and the Prophet ’08 Module
March 18, 2008: Shipping announcement for the Prophet ’08 Module
May 16, 2008: Announcement of DSI expression pedals, immediate availability
June 1, 2008: Poly Evolver Rack discontinued
September 24, 2008: Announcement of the Mopho, immediate shipping
May 20, 2009: Announcement of the Prophet ’08 Potentiometer Edition
June 2, 2009: Availability of PE conversion kits for the Prophet ’08 announced
August 5, 2009: Announcement of the Tetra, immediate shipping
November 5, 2009: Announcement of the Poly Evolver Keyboard Potentiometer Edition
Winter NAMM 2010: Showing prototypes of the Mopho Keyboard
March 15, 2010: Announcement of the Mopho Keyboard and the return of the Poly Evolver Rack
May 5, 2010: Shipping announcement for the Mopho Keyboard
October 1, 2010: Announcement of the Mono Evolver Keyboard Potentiometer Edition
December 2, 2010: Poly Evolver Rack discontinued
Winter NAMM 2011: Announcement of the Tempest
September 6, 2011: Shipping announcement for the Tempest
August 1, 2012: Announcement of the Mopho x4
Fall 2012: Mono Evolver Keyboard PE and DSI expression pedals discontinued
January 24, 2013/Winter NAMM 2013: Announcement of the Prophet 12; June 25: shipping announcement
October 15, 2013: Announcement of the Mopho SE, shipping later that month
December 18, 2013: Announcement of the Prophet 12 Module, first presented at Winter NAMM 2014
Spring 2014: Poly Evolver Keyboard PE discontinued
June 19, 2014: Announcement of the Pro 2, first presented at Summer NAMM 2014
August 11, 2014: Announcement of the DSM01 Curtis Filter Module, immediate shipping
August 12, 2014: Shipping announcement for the Pro 2
January 12, 2015: Announcement of the DSM02 Character Module, immediate shipping
January 22, 2015/Winter NAMM 2015: announcement of the Prophet-6; May 29: shipping announcement
October 14, 2015: Mopho, Mopho Keyboard, Mopho Keyboard SE, Tetra, and Evolver discontinued
October 22, 2015: Announcement of the Prophet-6 Module; November 25: shipping announcement
January 21, 2016/Winter NAMM 2016: Announcement of the OB-6; March 3: shipping announcement
April 10, 2016: Announcement of the TORAIZ SP-16
June 23, 2016: Announcement of the OB-6 Module; September 9: shipping announcement
October 13, 2016: Announcement of the DSM03 Feedback Module, immediate shipping
January 19, 2017/Winter NAMM 2017: Announcement of the Prophet Rev2 and the TORAIZ AS-1
May 18, 2017: Shipping announcement for the Prophet Rev2
August 29, 2017: Announcement of the Prophet Rev2 Module; October 25: shipping announcement
Strictly speaking, only the following instruments have been announced or presented for the very first time at NAMM shows: BoomChick, LinnDrum II Analog, Prophet ’08 Module, Mopho Keyboard, Tempest, Prophet 12, Prophet-6, OB-6, Prophet Rev2, and TORAIZ AS-1. That's clearly the minority of all the products DSI have released over the years. So there's no reason for panic if there won't be an announcement in about three weeks from now, as this has rather been the exception to the rule.