"That's the worry. Are proprietary routers going to get firmware updates?"
1) Routers don't ACK anything but packets addressed directly to them. ACK is a mechanism used by the receiving end to tell the sender which data it received (or didn't). TCP design is end-to-end - routers must only forward packets to their destination. If routers had to ACK, a) each router in the path should send an ACK, so the sender would get n ACKs and should know about the path b) it would be useless because packets could be lost after they passed the router c) the router would have to know what data were sent - a lot of states to keep!
2) Proprietary routers may not use Linux or BSD had have their own network stacks - which could be vulnerable or not. While SOHO routers may not get any update (many of them are already unsupported while sitting on a shelf to be sold), pro routers get updates until EoL.
Biting the hand that feeds IT
