I looked at Salsa's web site and read the instructions for these dropouts. It seems to me is that they are a very complex way to work around providing horizontal dropouts. They maintain vertical dropouts but allow the horizontal movement needed to obtain proper chain adjustment for IGH and single speed use.
To get that adjustability, you give up a lot of simplicity and the ability to use off-the-shelf racks and, I presume, fenders.
1. Where the rack mounts is on the bolts where dropouts pivot. Which means that there should be no change in geometry anyway as it's adjusted. So i don't understand why this creates any difficulty.
2. Even if it did mount near the bottom, the rack forms a triangle with the frame with one angle being hinged, so again i wouldn't see this being a problem! (And actually the rack is really more of a 4-bar linkage with the adjustment in length of the bars going from the seat stays to the rack giving even more adjustability!)
Maybe the alternator rack is permanently hinged to allow for that dropout movement while a normal rack would hinge during setup but would then be tightened down? I'm also betting that a normal rack will sit a little higher due to the attachment point being higher. It's my understanding that keeping the weight as low as possible is to your benefit, but i don't see these 2 inches being problematic.