I agree that theft is a possible issue. I was hoping the Amazon Echo might send an alert when offline which would make tracking theft fairly easy but, so far, haven’t found such a feature.
I’ve read good things about the Google Home but one advantage of the Amazon Echo Dot is that it’s only $49 and, so, a relatively low risk experiment. I don’t imagine that anyone would directly pay more for access to a voice-activated speaker. I could see it helping a bit with improving the customer experience, though, which could indirectly increase revenue for guests who enjoy their stay a little bit more and leave a slightly better review as a result. As @austinmodernluxury notes above, guests seem to enjoy playing music on them.
In essence, I view it as a delightful internet-era radio/alarm clock for listening to music, news, weather and setting a wake-up alarm. So, in many ways, the applications are quite mundane but still helpful for guests.