@MitchellJetten: A good move in the right direction. I think
@TrentTroop has the right of it, though, the lack of immediate feedback will definitely lead to more orders of "maybe-printable, maybe-not" models that will result in failed prints and frustrated customers.
From what I understand, if a model is definitely not printable in a specific material, that material will simply not appear on the model page when it is uploaded. This can be confusing to new users who don't expect that, however - it might be more immediately understandable to present the material in a "greyed out" manner, unselectable, so that users don't wonder what happened to the material.
A simple mark that there are problems that might cause the print to fail, as we used to get with the "yellow triangle" mark on the upload page, would also help to indicate that users should check the 3d tools to see what the problem might be and correct the model.
I can see how the current site design is meant to be a minimalist, streamlined thing, but as we've seen testified by so many users already, it actually ends up complicating workflow and failing to present vital information that the old interface handled perfectly well. You've made some good strides towards restoring that functionality, it shouldn't be hard to finish the job.