I came here to suggest the same thing. Even if it's not automated through National Highways, allowing users to press on the speed limit icon and then to select another speed limit in the same way we'd report a vehicle on the shoulder and then press it again to change it back when the variable limit ends would be very useful for timing drives and also understanding what the limit currently is. There could be a question to other users such as "speed limit still [X]?" so if someone erroneously reports, or if the limit is no longer accurate, it reverts to the default limit.

This would extend to other countries, where temporary speed limits exist for other reasons such as roadworks on a main road.

I think this feature would cut the mustard between Waze and other mapping softwares for navigation in the UK.

As an editor we are constantly bombarded with URs asking for a temporary speed limit change on Smart Motorways when there is nothing we can do to change this real time. A strong collaboration between National Highways and Waze could mean that Waze is able to update its speed limits on certain segments real time in reflection to its live feed, and hence the real speed limit.

I think this feature is a MUST for UK navigation due to the abundance of these road types.

Yes this feature is very compelling
Please add this

+1
And an option to start-stop marking the speed limit stretches so that Waze can display warnings to other Wazers only for the zones that has an imposed speed limit.