Hiring people in third-world countries to fill out captcha is already very easy.
For many accounts we already see today that a mobile phone number is required. Requiring mobile phone numbers is often enough of a link to real-world information.
Facebook for example does it like that.
While there might be some blackmarket sales of accounts for spam purposes I would be surprised if the accounts will be worth much and the risk of being labeled as a spammer by google and lose access to google accounts is large enough that I wouldn't want to register 1000 google accounts for purposes like that.
Google can decide to verify existing accounts. I think it's likely that in its efforts to avoid platforming spam, cybercrime and astroturfing, Google may decide to leave existing "reputable" accounts alone, but will ask for e.g. a phone number or other KYC for existing accounts that were basically never used, as an easy fix to the issue you're describing here.
It seems like these are unlikely to be very valuable. If they started to have a significant value, Google would just sell them itself?
You may have noticed that CAPTCHAs have become harder and harder. With the imminent advent of powerful multimodal AI, CAPTCHAS might soon be no longer be able to tell human from AI. The era of easy signup and free accounts might be at an end. It might consequently be much harder to get accounts set up and new cumbersome human-verification procedures may become the norm. Many current security protocols used in banking are already not AI-safe anymore.
One consequence would be that the internet might become less anonymous and less anonymous as accounts will have to be linked to real-world authentication. We already see a centralization of online identities around Google accounts.
A more interesting phenomena might be that accounts made before 2023 may become quite valuable. Does this mean you should stock up on gmail (and other internet services) accounts?
What do you think is the best way to prepare for a post-CAPTCHA world?