The proposal is for a way to propagate changes using Get/Set*Info_String/Value methods to corresponding items/takes in the same pool.
Perhaps a new function called 'Propagate*Info_String'/'Value' with the source object and name of the parameter passed as argument?
e.g.
Code:
reaper.GetSetMediaItemInfo_String(item, 'P_EXT:stuff', 'some_value', true)
reaper.PropagateMediaItemInfo_String(item, 'P_EXT:stuff')
all media items in the same pool will now have the same value for 'P_EXT:stuff'