This is a tracking ticket.
Given this list of proposed widgets to stabilize during the next iteration: P292
This is the list of BETA types which would need to be stabilized too because they either appear in their inheritance hierarchy or they are used as parameters, return values or event infos: P293
Each type is prefixed by how many times it is used (i.e. how many widgets use it). There are 128 types.
This is the hierarchical view: P294
Stable classes are removed so the hierarchy is a bit hard to read.
This is the script used to obtain the above info: P295
Remove the commented lines to get the hierarchical view. As it is now, it dumps a plain list of types which can be processed with sort and uniq.