Define "attach peripheral". Is wireless display over DLNA ok?
Smart TVs actually have many nice features many people don't know about, dlna being the most prominent. Universal remote being another of them, with my TV I just say I have device x on hdmi2 and the TV remote will then be able to do almost anything I need to control on that device.
The built in apps are usually crap but I do see the value in having the ability to install them, why should I have to buy yet another device if I just want to watch Netflix, the TV already has the processing power to do so. Although arguably a chromecast is practically free compared to the price of a TV.
TV ports are digital now, they could power and give control to another device. Just stick a port on the back for the box . I actually love the stick form-factor that's growing now, let's you hide the device and get the sleek appearance of a smart TV without the cruft.