I would like the same thing.
I am creating two maps. One at A3 and one at A1. The A3 map needs to have a different basemap to the A1 one, as obviously an A1 basemap would be too detailed at A3 and an A3 one isn't detailed enough at A1.
Apart from the basemap and scale being different, every other layer is the same and the projections and maps units are identical.
ArcGIS Pro already supports different scales, it just needs to support being able to switch layers on and off differently for different map layouts.
Was multiple map layouts always intended to just be used for multiple map frames? Are there any practical examples where one map frame would be used by multiple layout views?
If I wish to change a symbology and I have multiple map frames, it means I have to update both and keep them in sync. Far more to go wrong than having a single layer that I update. Is their a way of keep the symbology for multiple map frames in sync?