A couple projects tried to keep the sidebar icons alive using mySIMBL (1) and later MacForge (2) but they've sadly all been abandoned. (I think.) They never really worked all that well, requiring finder-rebooting and various shenanigans to get them to run (if memory serves.)
(1) https://github.com/w0lfschild/mySIMBL (2) https://github.com/MacEnhance/MacForge
The SIMBL on my website uses an unmodified SIMBLAgent binary taken from an older version of w0lfchild's mySIMBL (https://github.com/w0lfschild/mySIMBL). However, I recompiled his SIMBL.osax with 32-bit support added back in, since I use a lot of 32-bit apps: https://github.com/Wowfunhappy/MacForgeFramework
Quick note that I don't really understand this code, I can just tell you that it works, at least on Mavericks.
On Sierra, you can reenable favicons with MySIMBL [1] and SafariStand [2].
[1] https://github.com/w0lfschild/mySIMBL [2] https://github.com/anakinsk/SafariStand