You all are comfortable just enabling your camera for some random site so it can capture your face?
Present options to pick a username, email, social media, live text, live audio stream, live video, health data from a smart watch, teenage diary, ...
It already works in some way; e.g. even if one person has both a HN account and a Snapchat account, they would use these to talk to different people.
I showed it to a colleague from marketing as a 'look how bad up this is!' They asked 'cool, can we do that too?' sigh
Given, the different people require different levels of privacy.
This is also why privacy has been a game over for decades. Ten years ago or so, friends boasted that they don't use Gmail due to privacy concerns but happily email folks with Gmail accounts.
One group picture is sufficient, you can work from there.
ELI5 when you visit online they have a handle on you.
On a meta-level, this is the essence of social engineering: creating a seemingly harmless and fun distraction to get what you may really want.
"Consent to give me pictures of your face and movements" as a pop-up would probably spoil the fun a bit.
It would be swell if more of the web was made by passionate people to share knowledge for free. I know this is a privileged attitude as creating content takes time which is not free. But some of the best web sites are the ones without monetisation. We need a better monetisation system for the web that is based on people paying for content instead of people being sold as user data.