I have it on good authority that the Montrail Slipstream that briefly appeared on the Montrail website and which I previously discussed here is no longer in development. While I was pretty excited by the concept of the Slipstream, it is my understanding that the realities of the shoe (particularly the weight and technological deficiencies of the BOA lacing system) would have resulted in the shoe not living up to what I expect from Montrail shoes and it was precisely for that reason that the project was scrapped.
I remain very excited for the soon-to-be-released Montrail Nitrus. Last I heard, the Nitrus should be available in April.