First, I want one for just for the sheer beauty of it. Google has come up with something that appeals just by its looks. Long journey from the first G1 to Q.
Second, Google now wants to be in our living rooms n even kitchen. Long and unexpected growth path for what was once a information service
Third, Google wants full control. No multiple partners to built this device. In phones, Google struggled in providing singular user experience due to multiple partners n burned fingers, Google TV didn't take off. While Nexus phones n tablets were after thoughts, Q is the first product that will remain exclusively Google.
Fourth, Google wants to be Apple. Own the entire ecosystem from hardware to content. Only Google play store content and youtube. In, Future Q will certainly open up to players like netflix but still it will be via Google cloud.
Finally, While point 1 worked, hope the rest works in favor of Google.