Confirm boiler shutdown before closing last rad valve
If the Tado app made sure it turned the boiler off before it closed the last radiator valve then this would allow the whole heating system to have tado valves on each radiator.
In our house we have a nursery radiator which comes on regularly through the day and night. Because some radiators don't have thermostats (towel rails) they are also on whenever any of the other radiators are on. I believe this practice is so that the boiler water pump is not trying to run against closed valves. However, it would be possible to have Tado ensure the boiler was only on when a valve was open.
when a radiator valve opens, if its the only valve that's going to be open then it also turns the boiler on. It could sequence to ensure it confirms the rad valve is open before it turns the boiler on.
when a valve closes it could check if it was the only valve open and sequence the wireless receiver to turn the boiler off first.