I mention AR because browser extensions would work well on the web, but you'd only be able to do the same on mobile with a system that cooperates, and there's a slim chance that Apple and Google - esp. the latter - would allow something of the sort to materialize. Plus of course with AR you could take it to the streets!

As for the business model of this independent platform, one could still make a ton of money out of it as long as its revenue-generating incentives were disaligned from the review scores, and I really think that's not such a hard problem to solve.

Ohhh. Phone as browser in physical space, AR as extendible medium.... I like.

For the AR-ish part... Oh, widgets! Right? Like clock, or weather, or the news thing. Constantly (modulo performance) update what you're showing on the widget based on location. Or dynamic notifications; "this is how many reviewed locations we know of at this location".