If you can really make a 100% unconnected one, not even for firmware upgrades (just let me use that damn USB port), or Smart but with 100% Open Source firmware -drivers included-, and possibly sell it in the EU too, I'm in. I'll soon (2-3 months) have to buy one, and I'll be probably shelling out like 3-4 times the cost of a Smart TV to buy a signage display to connect to my Kodi based system just not to have spyware running in my next living room, so unless I'm a complete idiot, I guess there's a market for a lower cost one, even though as a consumer product it wouldn't be rated to last as much as signage displays are.

A final thought: Arduino and the Raspberry PI became the reference in the makers community, not because they were better and/or cheaper but because they were reasonably good and cheap, but most importantly they were very well documented and offered standard connectors that would allow makers to build their devices knowing they would be compatible with the new models. If you make a 100% Open Source dumb TV with a rear Open Source well documented connector allowing tinkerers to extend the device functionality beyond adding a TV box (which in most cases just moves the privacy issue one HDMI cable away), your product would be extremely well received by the tinkerers community, and probably much beyond it.