With CalDAV being deprecated, the more pressing question for me is, "when are they going to kill the free IMAP protocol?" Individuals who use desktop applications like Thunderbird or even Outlook never see any Google ads. The most sophisticated targeting advertising techniques in the world can't help if a company can't get your eyeballs on the ad in the first place.
If the trend does continue, I can envision a future where everyone will have to use specific "Google connector"-style APIs [1, 2] to access the various Google services.
I think you underestimate the amount of information google learns from your email.
What you bought, where you bought it, how much you paid, which emails result in a sale conversion, who you talk to, services you subscribe to, political affiliation, job status, career field, charitable giving, hobbies, and vices.
By using a Gmail account you willingly tell others to send information about you to Google.
If the trend does continue, I can envision a future where everyone will have to use specific "Google connector"-style APIs [1, 2] to access the various Google services.
[1] https://tools.google.com/dlpage/gappssync
[2] https://addons.mozilla.org/en-US/thunderbird/addon/provider-...