I took my time to somewhat read through polish threads here. I really needed a beer there. Afterwards I took some time to read a bit of a history. Lets give it another try now.
Thats a fair enough statement. Also diplomatic relations and warmongering around Europe covered. Not much left though.
UA: "Golden liberty" - conquered cities retain their cultural buildings. Social policy cost increased by 15%.
UB: "Seym" - replaces courthouse; half the build time, generates 1 culture, half the maintenance cost.
UB: "Cloth hall" - replaces mint; a city produces 2 extra gold, 1 culture and 1 faith per available luxury resource
All numbers and values are subject of change. I have not done the math there to calculate any sensible balance.
Now, I guess I have to "defend" this against "not polish enough" and "not cool enough" parties

. According to historical records, that are available to me, golden liberty was the biggest problem that completely stopped development of the country due to an unlimited freedom it gave to the upper class. However along with that Poland was the most open country in the Europe; accepting all religious beliefs and cultural spin-offs. Besides that there was a rule "Nihil novi nisi commune consensu" meaning "nothing about us without us". So for anything to change a local population had to gather and vote, which pretty much killed the country at that time. There is no denying, though, that everything from all around just blended in creating a one-in-a-kind country. It collapsed on itself later on, but CIV game is about altering the history right?
As for a "cloth hall", yeah its just an ordinary, old version of the supermarket but(!), location of Poland (right in the middle of Europe where all the trade routes were crossing, also with an access to the sea - very important trade route) made it special. The "anarchy" of the times was an ideal ground for trade bringing in the baggage of various cultural and religious exchange that were not allowed anywhere else.
I admit its hard to place Poland anywhere and not overwlap existing stuff. Presented setup should provide a unique play style not available in Civ yet. Even though the UA might seem like a big pain, if used right in conjunction with "seym" should provide some interesting opportunities. To make sure that civ is not one-directional the cloth-hall is quite powerful to counter UA vice.