Icons might be nice but when you have a lot of folders with all this different shaped and colored icons, it makes the UI too cluttered and noisy. Maybe if icons where all just grey, minimal (B/W) and designed with the same concept (as Material Design) wouldn't make such a mess of the UI. Also I would rather not to have icons at all and let us have a neater and cleaner interface with more white space and just text (eg: Pinboard).