To me that's more of an argument for GP's idea. Make it rational for them to care about it. Display a big "You can't visit this website because <ISP name> won't let you. Here's their email:"
Obviously it's not worth it for any website that matters to actually do this, but it's fun to think about.
It's more like the carbon tax. The companies with lazy network admins are "externalising" the cost of their outdated networking on the larger Internet ecosystem.
