They do point out that they will be monitoring how it’s used, and could adjust things later.
Sounds like corporate-speak for “if people abuse this, we’ll lock it down harder.”
Even if people are using it to share with actual family around the country, they may get caught up in future updates that remove that feature. Also note that any publisher can opt out of the sharing. If EA or Ubi or some other big company doesn’t like the lack of limits, they may be able to force Valve’s hand in changing the policy.
The idea is wonderful, but there are a ton sof ways this could end up worse than the old system.