I would guess some modification will be required with a modulating boiler, the thermostat should not turn boiler off/on but up/down yet the timer will still turn boiler off/on, so the thermostat will not be connected to the motorised valve as in old system but direct to boiler.
I have questioned without getting a good answer how one uses a S plan to control upper and lower floors when you only have the option to fit one modulating thermostat, as far as I can see one has to use electronic heads on the TRV and get rid of the S Plan as there is no provision to use modulating thermostats with the S plan, or control lower floor only.
It seems government is behind the times, insisting on split heating control when we have passed that point with technology, even the boiler manufacturers seem to be lagging behind, Vaillant I thing supports OpenTherm so likes of Tado and EvoHome can be used, but Bosch only have their own "Wave" thermostat which will only measure and control one room.
Will your system as you show work, yes it will, will it work with maximum efficiency, I don't know, theory and practice do not seem to match, all down to air movement, what doors are fitted, how much heat the walls store, so in my case the electronic head turned radiator off, but it was already full of hot water by that time, so room over shot the mark, fiddling with lock shield valves improved it, the TRV is bi-directional, however if not fitted to supply side radiator over shoots.
I have given up, moving house, new house is oil, so although modulating boiler 18 to 24 kW is really a laugh, so returning to old system.