One obvious feature would be to provide geo fenced Wikipedia or news feed.

Like what is the highest rated/longest Wikipedia article in the area.

Or maybe what's the 3 top radio stations and a link to them.

There is plenty of local content that Google does not surface

Geo fenced Wikipedia exists already, as a number of apps are available which offer regional maps with localized Wikipedia additions, see for example https://wiki.openstreetmap.org/wiki/OsmAnd

I could do that. Have additional information about the area based on the perimeter.

These are great ideas!

I am saying for it to succeed as multi-user, it needs to be useful first for a single user.

Twitter was never useful for single users.

Twitter started as an internal service for existing Odeo employees, so an unfair comparison if you're talking about cold, starting a social network. Twitter didn't start cold.

It was. Twitter used to send SMS and therefore notify others on what you're doing even without them having anything installed.