Content creators on PeerTube could do in-video product endorsements.. that's already a fairly standard practice on YouTube, which does support monetization.
It's a bit of chicken and egg problem though. To get in video endorsements, you need to get very popular. To get very popular, you need a more popular platform than peertube.
It depends. You obviously need a millions of subscribers to promote the 'appetite suppressant' lollipops - and you need a TV to promote the new life insurance brand. But to triple the sales of HackRF, a couple of thousands niche auditory is enough.
Sponsorships are only one form of monetization. The competitive feature for content creators here is ad revenue sharing.
The only thing I got from reading this write up is that it will be pretty easy for someone to create their own instance and throw ads on someone else's content.