I’ve looked at some of the results of having armor from multiple weight classes in the equipment preview, and it appears to cause conflicts in the texture of the armor pieces where parts of the armor would have swapped textures with others, or simply not appear. However, it seems like it would be easy for Arena-net to fix this issue with headgear and shoulder armor allowing us to transmute those items.
Complete cross class armor transmutation shouldn’t happen though, as it would make it more difficult to distinguish between classes, especially in PvP or WvW. I still support the idea of cross class headgear and shoulder armor transmutation.