This has been an idea probably on the minds of some VRChat devs for a long time now, and it would be lovely to see a simple way to purchase ownership of VRChat avatars and be able to download them in the SDK to customize them, or buy them and use them ingame.
Having an in-game catalogue would also promote creators to make content solely for the platform, and it would be really interesting to have an SDK where perhaps a higher rank such as known user and above, can think about selling authentic avatars for people to use all within the platform.