I also believe powder will be the big one a powder that has the advantages of Blackhorn and the capability of being ignited in any muzzleloader even with #11 caps and a bit longer burning period with more potential energy but not any higher pressure.
It is with in the capabilities of present technology to do this in a none corrosive non residue powder.
There will probably also be a sabot that will handle the .457-8 400 grain bullets to make very large game practical with a muzzleloader.