NVIDIA is not ruling out the possibility of the NVIDIA SHIELD Android TV coming equipped with Alexa integration at some point in the future. This is based on comments made by NVIDIA's Director of Technical Product Marketing, Sridhar Ramaswamy, to TechRadar, during CES 2017. While it does seem as though there are no current plans to add or make use of Alexa on the SHIELD as a default assistant, Ramaswamy was noted explaining that the SHIELD is an 'open product' and they have not "ruled out other platforms" and/or other assistants, including Alexa.
However, Ramaswamy was also noted explaining that as the SHIELD is an 'Android TV Box', their decision to make use of Google Assistant as the default assistant, "makes sense". Which does further add to the belief that there is no obvious plans for any alternative to be included with the SHIELD in the near or long term futures. At least not while Google continues to develop their Assistant and presumably, while Android TV remains the building block for the SHIELD. Although, if either of those points were ever to change, then it seems NVIDIA would be open to making use of alternate platforms.
Of course, while the NVIDIA SHIELD is likely to be a very hot product over the next few months and prove a good gateway device for Google Assistant, Amazon and their Alexa assistant has proven to be not short of takers recently. While NVIDIA and some companies did take the opportunity at CES 2017 to announce Google Assistant integration, the event was by large, much more Amazon-focused with a sheer majority of assistant-integration announcements coming through dealing compatibility with Amazon's Alexa. The number of products which were announced with Alexa support spanned product portfolios, with even the likes of LG announcing a new Alexa-powered fridge. Which overall does mean that Alex was one of the clear winners at CES 2017. Not to mention, does highlight that the assistant battle is one which is likely to greatly heat up in 2017. While also highlighting that as Google Assistant is the newest assistant to come through, it does have some way to catch up with the likes of Alexa in terms of third-party hardware adoption.