A PWA is just a Website.
A „Marketplace“ for it would be nothing more than a linklist.
When you think about it, this could be realized with the nostr protocol or something like stacker news
You post a link and when people think it’s useful then they can zap the link.
.. could be a way. Maybe I am naive, but I would love to buy from a marketplace and pay with Bitcoin to be honest. I’ve seen initiatives, but the UX was not nice. There needs to be more incentives in general for what you can really use Bitcoin for. Why not start small with used clothes or everything for the child and used tech? I think it would be a full time job to take care of this. There are funds that promote Bitcoin projects, that could jump in.
