Yes, Comcast is basically test marketing this Extreme 305 tier in the Northeast right now, to get a sense of what demand there might be for a premium-priced, residential, 300Mbps service:
From the Light Reading Cable article (»www.lightreading.com/document.as···lr_cable) about it:
Essentially, Comcast is fighting fiber with fiber. It's utilizing a business-class platform to deliver a high-end residential service as it tries to discover what sort of demand there is for an uncapped 300Mbit/s product that currently sells for US$300 per month. And, according to this statement from Comcast spokesman Charlie Douglas, it appears that Comcast will use the fiber-based approach as a placeholder for very high-capacity residential broadband services until it makes business sense for the MSO to make significant changes to its DOCSIS platform.