I definitely agree that IBM is not a strong contender. As for Google, I am more optimistic of their chances after the new announcements at Google I/O.
It is true that Amazon shines in the retail space. As I’ve written before in “Voice: The Gateway to Ambient Computing” voice/Alexa is just a new interface to their greater platform. To that end, Amazon has done a great job capturing the smart home market so far.
However, the strength of Google lies in its far superior advantage in ML/AI. Now that Google Assistant SDK is available and focused on being embedded in every system, Google Assistant’s “smartness” might sway customers from Alexa-driven Amazon platforms. Google has already unveiled their video calling features and they now support visual responses vis Chromecast-connected TV (see more notes from my Google I/O recap post). Maybe you want to bring up shared photos from your family’s trip over summer by voice. Maybe you want to look up directions and/or traffic information visually before you hop in the shower in the morning. Maybe in the future, Google Home/Amazon Echo is replaced by VR/AR devices that also support voice. In these scenarios, Google holds a major advantage. With this in mind, I think Google will be well-positioned for a competition with Alexa in the near future.