From TFA: Another attack on Samsung Smart TVs was published last week that used malicious commands embedded in broadcast TV signals.
So, even if it's airgapped, a tv that's been compromised in this way is effectively a hostile general-purpose computer with a wifi card running inside your house.
If this is something you would do for a Klondike bar, then go ahead. I'll keep my dumb TV and my Kodi box, though.
So why bother with a "smart" TV if you're going to be using an external computer anyway. Saving a few hundred dollars to spend on that external computer seems like a better investment. I run a "dumb" big LG TV hooked up to a raspberry pi running Kodi via LibreElec. I'm very happy with the set up in terms of functionality and price.
Edit: the attack via signal is linked from the article, reading now.
I'm in the market for a 4k TV with low input lag. If you look at input lag tests (e.g., http://uk.rtings.com/tv/tests/inputs/input-lag) you'll see that every single TV listed there is a smart TV, at least in the 43"-50" range anyway. In fact, are there even such things as "dumb" TVs anymore?
That said, I've done some more research and realised tha the LG UH6* range is actually also pretty good for low input lags and runs webOS to boot so I think I'll go for an LG instead.