Yes, this functionality and more is on the roadmap for the Visualize Cloud Library. We realize the importance of pre-made assets (appearances, textures, HDRs, etc) for our community and want to expand the library as much as possible.
What types of appearances do you specifically want to see more of?
I created an improved brushed aluminum that closely matches the material we make some of our computer parts from.
I've also matched some lightly textured plastics and other metals.
I guess I'd say "real-world engineering materials" should be the main focus.
Even Some SSS Plastics, a few popular variants to materials... etc.
Things that match and replace the most popular existing Solidworks textures would make sense.
(As in, I pick "stainless steel" in soidworks and it's replaced with a great version in Visualize.)
That would probably make the most happy users as it would reduce the learning curve before they get great results.
I must say, I really like the way the visualize browser can download from the cloud, that function seems well-implemented.
In training someone on Visualize, they got frustrated by the lack of many "photo studio" HDRs. I showed them the 10+ ones I had found on the net and they became much happier with Visualize. I imagine the vast majority of users want to simulate "photos" and that seems like a good way to reduce the learning curve.