The thing is, the Karma system directly collides with your goal of becoming ubiquitous.
I live in a small residential street where every neighbour who wants Internet has cable or fiber, so the chances of gaining significant Karma are very low. Let's also suppose I'm not a geek.
So, why would I pay $20 (+shipping?) for a new router, ask a friend to come by my house to install it, pay the electricity costs, etc, when in the end I'll still have to pay more to actually use it?
The Karma system eliminates the incentive for almost anyone except those living in busy streets to purchase and run their own router.
And this is helped by the fact that metered connections have all but disappeared around here, so a person with high Karma isn't actually "paying" anything for it, it's merely a rent that she can extract from the location of her property.
So I predict you'll mostly get users in city centers, which is where they are the less useful, since it's also where you can usually already get free or cheap Wifi.