Alright, let me give you a bit of insight into the Blackfoot design process, in hopes that it clears a few things up.
1) Originally, the Blackfoot were designed fairly differently. Research for the First Nations civs is very difficult for me. Basically, almost every First Nations team is very similar. They all use some sort of longhouse, wield similar weapons, became very powerful when they acquired horses, use similar forms of meritocratic government, and typically lived nomadic or seminomadic lifestyles. There are exceptions (patrilineal government, seasonal sedentary lifestyles, etc), but that's the jist of it. Coming up with UAs and UUs and UBs and UIs is therefore very hard. In many cases, the Uniques that I call "Unique" are not truly unique to the culture, but are a big cornerstone of the culture.
Part of this is the "fault" of the Cree, because they are so huge and so diverse, so almost every other First Nation's uniqueness has been absorbed into the Cree way(s) of life.
Basically what I'm saying is that if I could do it all over and had the skill to do so, I would pretty much build a whole new tech tree and whole new unit/building list and playstyle for "New World Nomads" and then give the specific civs variations from that. But that is not going to happen, not in this specific set, anyhow. (Unless you all think we can do that and are willing to do some serious heavy lifting to see it happen.)
So, back to the early Blackfoot. Early on, when I was gathering a list of fairly recognizable first nations of Canada (Blackfoot, Cree, Mi'kmaq, Ojibwe,) I chose them specifically to cover areas of Canada. The Blackfoot were brought in to be my "Plains"/Western Prairies team. As such, I have always wanted them to be focused on inland play, rather than coastal. Originally, when doing my research, I came out with three basic unique elements of the Blackfoot:
1) They had a taboo of sorts about water, due to their beliefs about water spirits, and the belief that the Blackfoot were allied with these water spirits, who gave them magic as part of their allegience, but that the treaty basically involved a clause saying "we don't enter their lands and they don't enter ours."
2) Like all other Plains nations, the Blackfoot Counted Coup. In history, this was done by touching a living enemy and then surviving to tell about it, ideally without getting wounded. This could also be done from horseback with the aid of a coup stick. Archers could count coup as well, but they had to do it with their hands, so it was still dangerous. As a person counted coup, they gained much prestige and, in the case of a war, the person who had counted the most coups became the War Chief, leading the Blackfoot into battle. This system put leadership in the hands of the person who was the best survivor, most cunning, dextrous, and intelligent, rather than in the hands of the bloodthirsty.
3) The Blackfoot were dependent upon the Buffalo, and built Pounds and used Buffalo Jumps to aid in gathering them.
Originally, I had the Blackfoot built like so:
UA) No work boats, gain faith from water tiles (later, river tiles)
UB) Barracks replacement. Allows units to Count Coup, which at the time gave various fairly random bonuses.
UB) Buffalo Jump. Replaced the Water Mill (a huge no-no for keeping water spirits happy) with something that required hills instead.
Once I actually started testing out the Blackfoot, some very serious problems arose:
1) Faith from water tiles is (unsurprisingly) extremely powerful. It would generate a ton of faith for the Blackfoot without the player ever lifting a finger. It also pushes players to play near water, which wasn't what I wanted at all.
2) The Barracks replacement felt terrible. An optional building that contributes a ton to your gameplay and basically makes you feel flat when you don't build it (and makes you feel flat until you build it) is a really bad idea.
3) Buffalo Jumps were too bland and furthermore too punishing if you didn't build your cities on hills. Plus, the Blackfoot are Plains people. Making them put all their buildings on hills made them feel more like Hill people.
At this point, I began to consider making the Barracks into a UA. It didn't feel right, however, since in Blackfoot culture any warrior of any kind can Count Coup. Restricting it to a single unit or even to a set of units seemed to be a huge mistake. I decided that Counting Coup should be on all of the time, which would encourage warlike play and feel better. Players should be going through the actions of trying to count as much Coup as possible, rather than being able to ignore it.
Having changed the UA into Counting Coup, I also went over Counting Coup several times, working it until it felt "right." Nowadays (newer info than TPang has,) Counting Coup works like so:
1) The first time you count coup, the unit in question gains a bomb of experience. This is enough to level it up at low levels, but if it is at high levels, it will not necessarily level.
2) The second time you count coup, if your unit is level 2 or higher (it will be,) the unit generates a small amount of culture, equal to about half its base strength.
3) The third time you count coup, the unit generates a twice the culture and gains a promotion that increases the power of nearby units. In order to gain this reward, the unit must be at least level 3.
4) After the unit has reached level 4, each subsequent coup count results in a one-turn Golden Age. Multiple fully legendary units can create long-term Golden Ages if you use them properly.
This version of Counting Coup pushes the player towards military play in order to scale up the levels faster, and encourages a lot of Coup Counting.
How do you successfully count coup? I iterated over this a lot (and am willing to share how I got here) but what I have now works like this:
1) You attack an enemy.
2) You go forward one turn, allowing the enemy to respond.
3) If, at the start of your next turn, you are very healthy (70+) and an enemy unit that is adjacent to you is not (25-), and you meet the appropriate level requirements, you will gain a coup.
Phew. Too much info, I know.
Back to the other parts of the Blackfoot.
The Buffalo Jump needed a rebuild. It was too bland and too hill-focused, so I chose to replace it with the Plains-focused Buffalo Pound. In order to spice it up, I had it spit out a Buffalo (because Firaxis gave us Bison, the Buffalo is a Bison with Gold/Food instead of just Food.) This way, you get a cool resource, but it can be taken away from you (pillaged.)
Overall, much better. The Buffalo Pound is no longer bland, and it pushes the player to play more in-land. On Plains.
You can still play on the coast, but it's more of an inland thing.
Now, what to do with the UA? I wasn't just going to drop the Sacred Waters thing. It was the cool distinctive cultural thing about the Blackfoot, more unique to them than anything else (Counting Coup is done by the Sioux and the Cree, too.)
The problem with UIs is that they can be duplicated over and over and over, making it hard to balance them to your cities. With food and prod, and to a lesser extend culture, this isn't too bad, but with Faith it gets powerful very quickly. So, a second UB. Overall, I figured that the lack of a UU wasn't too terrible given the awesome war-focused UA.
Eventually I settled on the UU being a river-requiring shrine. It feels good and pushes the player to build their cities in certain, typically inland places.
So, why the Work boat ban? Largely, for legacy reasons. I've been toying with taking it out and nerfing the Nato-oh Siskoom down to less Faith generated.