If I want a smart toaster, smart oven, smart anything else, I still don't see a good reason for these devices to have unrestricted internet access. Most of their functionality is mostly useful on a local network basis, not over the internet. Even then, they don't need to be able to access any websites, just a control device like my cell phone if I want to say turn on a coffee pot on my way home for company.
While that might not call for extreme encryption or anything like that, simply not letting the devices be capable of accessing anything else over the internet would solve most problems. Also, they can't DoS if they're forced to only be able to send/receive a limited number of packets per second, like, say, one? A coffee pot doesn't need a lot of internet bandwidth nor low latency to be turned off and on remotely.
That's what gets me about these IoT security problems. They're so incredibly simple to solve. Limit their capability in hardware/hardcoding to only be able to do what they need to be able to do and even if someone gets control of them, their malicious capabilities are diminished by many orders of magnitude. Make them only capable of connecting to the remote control device (cell phone) and they can't even be used to attack corporate or government interests, assuming corporate/government employees use separate work and personal phones like they're often supposed to. You generally can't exploit your way around a hardware limitation.