They already make "dumb" monitor controller boards for almost every panel in existence. The difficult parts would be:
1. Designing a shell that is unique enough but simple enough to pass muster for the average person. Aesthetics matter, after all.
2. Incorporating a remote that had the features you want without directly copying another design, and making it fully functional with the TV brains
3. Finding a microcontroller that can be purchased at the appropriate quantity that is able to handle the latest features that you want without requiring internet connectivity. (HDR, Post Processing, Dolby/Atmos/Surround, etc)
4. Getting the appropriate inputs to handle all of the expected inputs for at least 90% of your target audience's expectations
5. Getting the finished product UL Listed and fully evaluated by the appropriate licensing bureaus.
6. Doing all of the above without causing the TV's price point to explode well past the point where your average target purchaser can or would choose to afford it when less expensive brands exist that have reliable warranties or customer service or a name to live up to.
Should you pass those bars and have a modicum of success, then you will have to fight off all of the competitors who will leap at the target audience you've uncovered, releasing dumb tvs at price points you may not be able to match with the goal of driving you out of business even if it costs them money so that when the next cycle comes around customers will have no choice but to purchase their products again.
I don't know if anyone remembers the brief craze there was for off-brand Korean monitor imports a few years back.
Basically they had similar panels to the then-current 1440p 27" Apple Cinema Displays but were usually "Grade A-/B/etc." instead of A+. They had the flimsiest, crappiest cases and most primitive controller boards (i. e. no OSD or multiple inputs on many models, just keep tapping the button and trying to get the brightness where you wanted it.). I think the original market for them was domestic, and you pretty much had to order them via eBay or sketchy small retailers.
I suspect what did it in was collapsing prices for mainstream-brand monitors, and a choice-paradox problem (there ended up being dozens of seemingly identical units to choose from with different cases, so the market was probably sliced too think for anyone to succeed).
But the concept is completely viable here. Remember that the name brands have major cost centres you don't-- advertising, a high-touch retail sales channel, the R&D on smart features.
TBH, I'm surprised you don't see more higher-end TVs without speakers. There's always going to be physics-related problems with trying to have really decent speakers in a 5cm deep set. You can target the demographic of people who already have competent audio systems AND save on the BOM!