Public avatars have a certain standard they need to meet, but private avatars, which more and more people are getting every day, do not. Some people are even using this to get around the performance check now that their public avatar worlds are disappearing. Right now I believe the maximums are 10 materials, 50 Dynamic Bone Transforms, 3 Skinned Meshes, and 2 Dynamic Bone Colliders.
If all avatars are "checked" on upload, similar to how public worlds are now, and are marked as either "Pass" or "Fail", it would allow users to block avatars that don't Pass under a performance setting, similar to the Shield system. Those users with avatars that fail the check are still able to be uploaded and be seen by people who want to see them while the people who don't want them to affect their performance can easily hide them.