I see the problem,
we are looking at how the air circulates, not just a spot temperature. So heat leaves the top of the radiator, goes along the ceiling down the opposing wall, and along the floor back to the radiator, so the sensor needs to be on that route, putting a thermostat 90° from that path, and it will not reflect the heat of the room.
I tried with a wireless thermostat, placing it in different areas, to see how it worked, room got very cold, as darn cat sleeping on the thermostat.
However, I have one boiler, and 14 heated areas, using the lock shield valves we can at say 22°C in the target area, arrange other areas to heat to a percentage of that temperature, but change it to 17°C in the target area, and all those percentages are out, the TRV (thermostatic radiator valve) can help, we can set
the maximum room temperature, and measuring near bottom, and to one side of radiator ideally placed to measure the return air, but it will not fire the boiler, you can however get versions
which will fire the boiler through a hub, so what we are looking at, is how far to go. While heating is running, the movement of air means the room in general gets warm, but before the heating starts, so little air movement, we can get cold spots, so against the wall under a window will be colder, if this is where we are measuring the room temperature, then the boiler will start a little prematurely, as to if this is good or bad not sure, but you can get systems where the sensor is not in the TRV, and even TRV heads which also measure water temperature and compensate for heat direct from radiator.
So nothing to stop one having no wall thermostats and use the TRV heads to control the heating in every room, but we tend to look at cost, and also question if a boiler will work well if asked to output just 2 kW, I am an electrician so can't really tell you about boilers, but in my main house, every room but bathroom, has programmable electronic TRV heads, of them only one can call for heat, I also have two wall thermostats, one in living room and one in hall which can call for heat, so three locations in the house can cause the boiler to fire up.
Looking at near enough engineering, at £54 each I could fit another 9 Wiser TRV heads, but the cheaper eQ-3 which cost me £15 each in 2019 seem to be doing a good enough job.
I have 5 of the TRV heads, and two of the wall thermostats, which I can view and alter the temperature and schedules worldwide as long as I have internet.
But oil bill for the year around £600, only used for half a year really, so around £22 a week on heating, lowering the temperature will reduce the bill, so may save £12 a week on fuel, and £25 will not really pay for a better control system.
I had the same argument with geo-fencing (that's auto turning off heating when it detects your phones are not local) seemed great in theory, in practice, never reheating the house in time. So it has been disabled.
I have a flat under the main house, it also has a cat flap, and heating turned down to around 10°C just to stop anything freezing, we find our cats often prefer the cool flat to the warm house, I often walk in to see our male flat out sleeping in the middle of the floor.
And the black & white female will leave the house by chip reading cat flap, but wants letting back in at the window, even with the catch sellotaped down, the other two will go in and out, but Sible only out. But will go in and out of flat. The problem is we have a feral cat visit with catch sellotaped down, and eat our cats' food, but this time of year we turn a blind eye.
