It's possible (for now, at least) to revert to the old UI on jailbroken devices running the latest update. To do so, make the following change to /var/local/CHROME_CONFIG:
Code:
-isKPPChromeEnabled=true
+isKPPChromeEnabled=false
chromeReleaseVersion=1
isDebugMenuEnabled=true
From a quick look at the upstart jobs, this has something to do with the upcoming Bellatrix/Malbec Kindle; presumably the new UI isn't fully functional on this device and must be manually enabled.