The most likely interesting consequence will be companies burying a line in the ToS saying they can deny you service if you use a tool to reduce your opportunity costs of sitting in a hold queue.

The purpose of a hold queue is to reduce the number of customer service calls a company has to field. They will not take lightly to any service which defeats this.

Alternatively, they'll hire staff to answer the phone, say a few words to break out of Google's hold music detection algorithm, then put you back on hold, this time with ads instead of music. Repeat every few minutes to make sure you're still stuck on the line.

There's no limits to what's possible when you realize the purpose of anti-customer service is to harm customers rather than help them.