Very cool. In practice, unless you live next to a coffee shop, there'd almost never be anyone connected to your xfinity wifi network, so you'd get the full bandwidth anyhow. Although, if your neighbor has xfinity wifi, it'd be a smart way to leach off your neighbor's bandwidth.

Also, because your router is a routed client of the xfinity wifi network, I'd imagine there'd be a big increase in latency. It'd be interesting to see the before/after speed test results.