I highly agree with this!
I also think there should be an option for them to be thinner. Tabs are sometimes fantastic to work with as you can switch between many documents easily at once, but I tend to use Subwindows just because they are so large and I find the Krita-icons unnecessary and almost distracting. The Krita icons on the tabs don’t inform me of anything, and it’s some of the most eye-catching elements in the UI.
I really like the idea by eishiya, it would inform me of what file type it is, which is handy, and be less distracting.