In answering your three questions, I think you have the answer to the first one covered.
The answer to your second question can be deduced from the above discussion. Very few inks (blue-black or otherwise) have iron gall content. You can buy dozens of blue-blacks from Waterman, Sheaffer, Parker, Diamine, Iroshizuku, Platinum, and so many more and never find iron gall content. I've found the opposite to be true! I've carefully searched to find a few inks with iron gall content. And these IG inks are growing on me and finding a place in my daily pen carries! IG ink works well on the cheapest and worst paper, and the dry ink rarely feathers and never bleeds through the paper. It's a great ink for the office environment.
In my short experience with IG inks, I've haven't had any problems. I treat these inks as high-maintenance inks and give them a very thorough flush and dry cycle when I rotate the pen and ink out of use. I'm leaning toward a small group of pens that will carry IG inks to see how they act over time. I haven't found anything different from my experience with highly-saturated inks.
If you are looking for inks with similar characteristics, nano-pigment inks may fit the bill. Like IG inks, nano-pigments should not be allowed to dry out in the pen, should be carefully cleaned before using, and should not be mixed with other types of inks.