Reading Kant ("On the Proverb: That May Be True in Theory, but Is of No Practical Use"). One smart mofo, no doubt. What strikes me is how little liberalism has gone beyond his formulation of the rule of law & his conception of political legitimacy.
Certainly, citizenship is no longer restricted to male property owners, but that was accomplished more by economic changes than by a change in principle. Women and wage-laborers ceased to appear as dependent upon someone else for their economic existence. As capitalism became the dominant mode of production, labor-power had to appear as property equal to the tools and cottage of the artisan, or the field of the small farmer. Couldn't very well admit we were driving people into property-lessness, could we? But, like I was saying, this doesn't change the principle of mutually independent citizens.
Likewise, folks like Rawls have spent an inordinate amount of energy fine-tuning the sorts of things people can be thought of as possibly agreeing to. Nonetheless, the hypothetical justificatory schema remains the same.
There are new models of liberalism proposed all the time, but when you get past the fancy gizmos and new paint-jobs, and start kicking the tires and looking under the hood, you find pretty much the same engine.