Given that most of the Internet connected smart devices (SmartTV, fridges, home routers, set top boxes) are running on top of some form of Linux kernel already, what's he on about? These are the things that are getting comprehensively hacked, and mostly it is mistakes in the software stack above that is to blame. Whatever way you look at it, it's poor design, implementation and maintenance of firmware that is the root cause, not the lack of Linux inside.
Even if the firmware was standardised and opened up, how's that going to improve things? The result would be that one single flaw would allow hackers to breach all devices worldwide, not just one family of routers from one company. Sure, one single fix would deal with it, but that's not comforting. Imagine if all home routers got compromised and the attacker disconnected them all from the net. How then would anyone be able to get the fix?
If firmware became a standardised open platform there would be pressure to have things like virus checkers, etc running on them. It's happened with Android, why wouldn't it happen with standardised linux based firmware on other devices? And how would old devices be supported? The consequences are that there would be new firmware versions that won't run on older hardware, so we'd have the "Windows XP" style of obsolescence problem on everything, not just our desktops.
So it comes back to good design, and a commitment from manufacturers to maintain and improve their firmware and hardware. Having a real "Read Only" switch on the device so that a hacker physically cannot alter it or install malware would be a very good start.