If you haven't already, check out https://github.com/duke7553/files-uwp/pull/96 for a sneak-peak at the new designs for Files UWP. Your feedback and concerns are welcome! Please discuss high-level, conceptual ideas here and lower-level, code-related ideas on the PR itself.
Thanks everybody,
Luke Blevins
Developer of Files UWP
Just a thought, you might want to implement rounded corners around the app as that seems to be the current things in Windows.
@yaichenbaum Perfect timing. I just issued a commit ~5 minutes ago that starts this process. Also, instance tabs are nearing completion unless I run into a bug. I'll update the picture on the PR to reflect these design changes so far.
@yaichenbaum Not done yet... ;) In case you were wondering, the ribbon item selection indicator, Favorites item cards, and PathBar are now rounded. Drop shadow will come back eventually to the Ribbon pane.

Looking really nice!
First newui snapshot is now available.
I think the sidebar should be less transparent. Maybe like the Settings app.
newui has been completely merged into master now that it's stable.
A few settings I'd like to see implemented:
Hello @UltimateSky,
Please open an issue report for ideas 1-3. Idea 4 would not be practical because going through a folder and its sub-items is computationally intensive, and would slow down the loading of larger directories. This will, however, come to the properties dialog.
Thanks!
Closing this - since the first phase of the newui has shipped.
Most helpful comment
First newui snapshot is now available.