The nice thing about making scimitars light is that then you do get weapon finesse for a medium slashing weapon... one of the best medium slashing weapons, actually. Not for free, but then again, swashbuckler is a pretty good intro into this class.
The only problem with trading spring attack for ITWF is that it's third level in the class... which means that you have to have at least 8 BAB at that point... two levels later than you would otherwise qualify for the feat. Kinda crappy. I'm not sure I can convince my DM to make ITWF first or second level, but I'll give it a try.
While whirlwind attack is cool... it rarely comes in handy, in my experience. If you can kill everyone around you in one hit, cleave is almost as good, and if you can't, it's better to concentrate your attacks (which will be plentiful). And the last thing this class needs is another freakin' feat to take.
-The Souljourner