I just quickly threw together another Twitter for Mac app replacement icon, inspired by the newest iteration of the Share Icon found in iOS 7 Beta 5: http://www.macrumors.com/2013/08/06/ios-7-beta-5-tidbits-icon-settings-redesign-new-control-center-options/
Feel free to download the attachment and replace the original. Instructions are in the description of my first replacement icon.
Disclaimer: It's just approximately rounded corners, no superellipse.
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