Four displays it total on this MBP 9,1:
(1) 15" Built-in
(2) Thunderbolt 27"
(3) 1080p 23" via UGA-2K-A Rev B
(4) 1080p 23" via UGA-2K-A Rev B
OS X 10.9.3 Beta (Version 13D12)
DisplayLink 2.1 Mac BETA Edition
(must download from here:
http://www.displaylink.org/forum/showthread.php?t=61983, release version does *not* work)
All displays work as expected. No flickering. Only known artifact is missing apple logo on menubar for displaylink monitors.
Good luck!