Some textures still have not been updated to match the current style of textures. The main problem is that they have far too many colors that are too similar to each other to justify their inclusions, which in-turn makes some of them look plastic-y or too noisy. I've included a list of some the outdated textures that I have noticed below:
Blaze Powder
All Shulkers and Shulker Boxes
All Stripped Wood
All Wools
Handles of both Torches
Lever
Tripwire Hook
Chests and Trapped Chests
Widgets
Seeds
For feature requests/suggestions, go here.