½ of these comments asking for AirPlay, the other ½ asking for Android TV or wtf Google is calling it these days. Next someone will want Roku, while someone else wants Amazon, and we’re right back to where we started.
The purity of your idea is in the dumb TV. Don’t put a Raspberry Pi on the back, don’t build a mini-ATX PC in.
5 HDMI ports. Power. That’s it. People can bring their own set top boxes and everyone will be happy.
* people who want a completely dumb display with a bunch of inputs, as you say
* people who want a display with some smarts but that is "open", can be "hacked", etc
I totally understand the desire to have more things to hack, but there are already numerous little boxes, pucks, sticks, etc to scratch that itch. What's really missing is a way to get a display that doesn't have any of that at all and also doesn't cost 5x because it's made for commercial entities. (Incidentally, my early research suggests a lot of commercial displays actually have "smart" BS in them already, it's just more targeted at device management than serving content-based ads, so that inflates the cost if I'm not going to use it.)
EDIT: formatting
* people who want a completely dumb display with a bunch of inputs
This leaves the option to hack it with whatever input device the user sees fit.
It separates out the input box from the display (makes it easier to plug things into) and allows just one cable to come from the TV. You can also have a lot more ports this way (8 HDMI?)
Samsung has a TV that implements something like this (of course it has all the rest of the smart crap too that you could nix).
Also this makes it easy to potentially have upgradeable/future input boxes with new ports without having to modify the display.
It's still 'dumb', but I think breaking out the inputs is a better design.