Add the option to add an attribute to the vertex format for every element in a 'bpy_prop_collection'

[bartteunis]

A good example would be values of the vertex position and normal for the morph keys.
This is complex and likely requires an index into the collection.

[bartteunis]

Technically, what needs to happen here is that a vertex attribute gets added per element in the collection.
For e.g. shape keys, this would mean the following:

# The endpoint 
endpoint = mesh_data.shape_keys.key_blocks['Basis'].data
# Lookup of value as before
value = endpoint[vertex_index].co

Note how this does require the name of the key block/shape key to be known.

[bartteunis]

Another one is mat.node_tree.nodes['Principled BSDF'].inputs, i.e. the list of inputs of a shader node (or simply a node in general)