Sadly, it sounds as though Comcast will have the market for Docsis 3.1 modems to itself for the foreseeable future. You won't be able to stop at Best Buy and pick one up for yourself, and just connect it to the incoming line, as you can with 3.0.
Which means we'll have to buy/rent Comcast modems, at some exorbitant cost, and be subjected to their ever-expanding "dual" modem plan that plants a WiFi hotspot in every customer's home, while the customer picks up the tab for the split bandwidth it demands.
I'm looking at you askance, Comcast.