With a tank stat the stat comes after the programmer, so it would work the same as any other programmer, this is the problem, you would not set Hive to gravity, even though it was, why hive or for that matter any other programmer connects the com to line in internally can removes the option to wire like Nest I don't know.
The whole central heating control system seems to have gone crazy, I have looked for ways to control and each manufacturer seems to have a problem some where.
EPH do an opentherm thermostat which can be run as master/slave, seems great, then you realise there are no TRV heads to work with it.
Nest also has no TRV heads, they did use Energenie but removed support.
Energenie have the wall thermostat telling the TRV what to do, every other system works the other way around.
Other than EPH not found any where you can have zone valves (Not TRV) and Opentherm.
The fan assisted radiators do not control flow rate, really good radiators for kitchens, but will not link with systems using TRV heads for control.
The list goes on and on, there does not seem to be any one size fits all, to be frank I really don't know why you would split a normal house into zones? OK this one the flat under the house is not heated most of the time, so turning off whole flat does make sense, but the main house has 7 rooms not including bathroom hall landing and stairs. Every family will have different use for the rooms, and likely the use will change over the years, so we have kitchen, living room, dinning room, office, craft room, bedroom 1 and bedroom 2. So bedrooms only need heating at night and when sick, but craft room and office often used during the day, the dinning room and kitchen will likely be first rooms used on return home. So unless you have two pipes feeding each radiator so you can select which zone that radiator is on, two zones is useless. Makes far more sense to use the TRV heads to form zones so every room is its own zone. So I can understand why manufacturers do not make controls to work with zone valves, with programmable TRV heads there is simply no point in having zone valves.
But heating is not the only thing in the house where common sense seems to have been lost, the idea of just 2 RCD's controlling whole house also seems daft, if I have a leak which means I need to turn a socket supply off, either I want all live conductors switched off, or I want the RCD only controlling that circuit, why all houses don't have RCBO's fitted I don't know.
Why is there no 16 amp FCU so ovens can be fused independently from hob, the list goes on.