I found this thread because I assumed this must already be an option in Krita and I just didn’t know how to enable it 
I’m pretty new to digital painting and I started with Krita a few months ago, so I didn’t have any basis for comparison. Now, after having played around with a few other programs and come back to Krita (which is still the best!), I have to say I sorely miss better brush previews. It makes such a huge difference in brush discoverability!
Just seeing another little picture of a paintbrush doesn’t really tell me enough.
Also, as a brand new user it actually kind of limited my thinking – it didn’t occur to me for a long time that I could use a “pencil” brush at a large size for texture, for example. (Silly, I know.)
This ^ exactly. I’ve started creating a big doc just filled with labeled brush swatches so I can actually find what I’m looking for.
Or using Deevad’s brushes, which at least have pre-made swatches I can refer to. Or the Concept and illustration bundle, which has useful brush icons already.
I’ve actually toyed with the idea of forking Deevad’s brushes just to make new icons for all of them in this style … but it seems like it should be automate-able!
Meanwhile, until this feature exists – if you’re a brush author and come across this thread: please consider making your brush icons in the “Photoshop-ey” style!
I, for one, will be very grateful 