Up to ISP's to block
The only way I can see it being fixed is ISP's blocking the traffic.
Cue discussion about how to ID the traffic, how to implement blocks etc.. No idea - beyond the scope of this comment at the moment.
Yes, there'd be cost for the ISP's.. but there's cost for them too if this issue balloons.
What other way is there?
We can't expect manufacturers to do much - they may not be around long.
Responsible manufacturers who're in the game for the long haul will make patches available promptly, and for a reasonable time after the device has been sold. Irresponsible manufacturers will soon see their devices blocked, and word will spread to avoid them like the plague.
Joe Public (i.e., your grandfather and mine, people who just want stuff to work) aren't bothered about things needing updates, so long as they happen automatically, or can be triggered with the minimum of fuss. Bleating on about "if you putting a server on the Internet you should damn well know how to patch it blah blah" is useless. Like the roads - the Internet has some tools/clueless individuals on it - but it'd be a pretty lonely place to be if it were filled with just us geeks.
Consumers should be able to use this stuff, and it should "just work". If it doesn't, us geeks who think we're all clever are pretty much proving we aren't.
You shouldn't need a computer science degree to plug in a webcam and check your dog is alright at home, or to switch your heating on before you get in. And the argument isn't about who'd want to do said useless tasks - it's about making it work for the people who do want to do it. The Internet is theirs too.