rotorblades The min clean speed in most aircraft is a variable depending primarily on weight, thus a lightweight 146 can fly slower than a heavy RJ100.
Your question suggests that you are making an assumption in order to help the aircrew; a good idea, but what is the objective?
If ATC require a slower speed then they should request it; if the aircraft cannot manage that speed clean, then flap etc can be selected, or if the crew are unable to comply they should inform ATC.
Similarly if the crew require a specific speed they can make the request; there are several communication possibilities – “request speed xxx if able” – “request speed xxx due to weather” – “Emergency, I will maintain speed xxx”. ATC normally do their best to help requests and have an exemplary record in emergencies. All that is required is clear and concise communication.
Perhaps those crews who wish to keep the aircraft clean are unfairly imposing on ATC’s flexibility; if ATC give too much then workload and safety may suffer, what price a near miss, and whose fault is it.
Why should crews need to stay clean? It might save some fuel, but at the expense of increased workload or risk; it would only take one nasty incident just below min clean speed to upset the fuel economics argument. Higher speeds reduce the time available for assessment and planning for both the crew and ATC; turn radius is higher, etc. Perhaps time is the issue, but the same applies, just consider the number of accidents and incidents that involved an attempt to save time; time is not money especially if you have an expensive accident.
Thanks for your consideration, but I would prefer a smooth flowing and safe traffic pattern rather than ATC attempting to prejudge the aircraft weight, min clean speed, etc. ‘You can’t keep all of the people happy all of the time.’
P.S. if it is Thames Radar into LCY then 146/RJ crews need to dirty up and reduce speed earlier than normal for their steep approach procedure.