So, you shotgun hunters explain to me why .410 slugs have not been developed into the premier hunting round 
I would think that you could use the smaller .410 to get closer to true rifle performance then the enormously heavy 12 gauge slugs. It seems to me that all that ridiculous amount of weight in the 12 ga slugs is what really puts the limitations on shotgun hunting as far as range is concerned. I would think, that you could use .410 to get a lighter slug with a greater ballistic coefficient, and have more then enough room for the need gunpowder.
IMHO - When using a low pressure cartridge, (pistol or shotgun) weight has the benefit of momentum which gives better penetration. Using a lighter slug even if you got the velocity up over 1900fps, may get the job done but at what cost? (to the gun and your wallet)
You still have to keep the pressure DOWN for shotguns. They don't have the steel mass or strength of revolvers let alone rifles.
Shotgun slugs have gotten better by using sabots, but the 410 is the redheaded stepchild of the shotgun world.
Too expensive, ammo is harder to find and a 410 won't and can't do what the same load will do out of a 12 gauge. Move up to 12 mag territory and it's no contest.
Have you priced a box of 410 ammo lately?
Side note, why anyone would use a 410 shell in a Taurus Judge instead of an honest to goodness thumper 45 Colt is beyond me unless the recoil is GREATLY reduced and/or you have serious overpenetration worries.