There could be an opposite avenue: ad-free Google Premium subscription with AI chat as a crown jewel. An ultimate opportunity to diversify from ad revenue.
The low operating margin of serving a GPT-4 scale model sounds like a compelling explanation for why Google stayed out of it.
But then why did Microsoft put its money behind it? Alphabet's revenue is around $300bn, and Microsoft's is around $210bn which is lower but it is the same order of magnitude.