Your TWF additions are an improvement, but still bring to bear one of the big consequences of being a dual-wielder, which is feat cost. The standard TWFer is still going to have to burn 3 feat slots, although the extra benefits of having the TWF, ITWF and GTWF feats do help to make up for this, that's still 3 of your base 7 slots you need to burn. Maybe too me this is more of a problem than it is to others, but having to burn half your feats seems like a rather big disadvantage. A single scaling feat seems like it would be much better considering the other downsides of dual wielding (RNG, cost of obtaining and enchanting two weapons instead of one, etc, etc).
Of course, if you're a class that already gets these feats for free, then you're in the clear really, but not everyone wants to play a Ranger.

That said, I'm rather fond of your Sword and Board feats, and I'm eager to see what the Two-Handed Weapon and Single Weapon chains look like.