Some people care about bling, a lot - it would be up to personal preference. If we created a basic framework to build on that is the same for everyone, that might be a good start. Here you can make basic appearance changes, think of the Sims games…
For more advanced users, you could import your own avatar - this notion of transferring your character between metaverses will only get more important as the online worlds start to merge. Not everyone will want to embody a ”human“ appearance…think of VRChat. If I want to be a floating bubble of iridescent light, I should be able to import that as a file from blender (exact guidelines could be provided if the avatars get more advanced if we incorporate movement, for example walking or running around).
People are buying „avatars“ such as crypto punks, bored apes, binary bob’s etc… you should be able to advance these into virtual reality avatars.
Regarding the idea of standing up for causes rather than fashion - the two go hand in hand in my opinion! You could change skins or alter appearances with coding using real time data, for example let‘s say you are a big DeFi fan and wanted to project the fluctuating price of Tezos onto a plane T-Shirt… the item of clothing would then change to project a number that goes up or down with the market economics.
Those who know how to code this kind of stuff could open up „boutiques“ to sell NFT‘s which hold the info to make those changes to your avatar - you would only need to "apply“ it in the AVATARBUILDER.
Look at CodeMiko VR streams where her viewers can pay to change the appearance of her avatar mid stream, there are lots of ways to do stuff like this with live / real time info, also making it interactive and getting your fans / followers / collectors involved.
How would you visually interpret a cause?