GG, the intent may be good, but the resolution is flawed. First, what's the definition of a "modern shotgun"? Browning will flat out tell you not to shoot steel in a Superposed, and they were manufactured into the 1970's. The information that accompanies my Parker Reproduction 12ga, made in the 1980's, says that steel shot should not be used in full choke barrels. Second, while the cost of steel now approaches the cost of lead hunting loads, that is most certainly not true of any of the other nontoxic loads--which would have to be used in all "vintage" guns, not to mention some "modern" ones (like the Superposed). Third, as I mentioned previously, if secondary lead poisoning of eagles used to be a problem, that problem has quite obviously been solved. No need to do any more studies to tell us that we have a lot more eagles now than we did 15 years ago.
The road to hell is sometimes paved with good intentions.
