while thinking about collada (and implementing an c# accessorframework) we had some serious problems with the matrixstack.
I see that the stack is very usefull for the exporter-projects, because they can project 1:1 special animation features of the different 3d modelling packages
for viewing/rendering applications the matrixstrack is not a problem because they can bake it to a single matrix for every timestep after the animations are applied
we see problems with applications that want to edit/change the content (specially animated objects (e.g. with multiple skew, rotate, translate, …)).
Ask the Importer programmer of the 3dsmax and maya plugins. Its almost impossible to match an animated dynamic matrixstack to a static stack every modeling tool is using. So we suggest to limit the matrixstack in the COMMON Profile to the following or a similar stack:
(Maybe a 2nd representation as a matrix (16 float) can be allowed
Maybe for cameranodes an other fixed stack should be defined)
In my Eyes its worth to thing about this, because i do not see the anyone uses a skew animation nor a so exported file can be read in any other existing 3d modeling package correctly in the future.