Think this through though. You can't arbitrarily increase the bore, or you're shooting bigger, heavier, lower-BC bullets. Likewise you can't keep extending the barrel, as nobody is going to hunt with a 100-inch barrel.
I'll put it this way then...We've nearly reached the PRACTICAL limits.
While you might not think pyro and 777 are performance equals of BP, they are a heck of a lot closer to BP than smokeless.
Who said anything about "arbitrary?" The majority of sabots shot today are .50 caliber, .45 caliber projectiles. Going to .54 caliber, there are certainly 45 / 54 sabots of last formulation available. Same,
identical bullets can be fired, and currently are.
Ever shoulder or fire a Knight Extreme .52? It weighs LESS than a Knight Extreme .45 or .50. Your opinion may be that synthetic flammable solid propellants are "closer" to blackpowder-- but they aren't "powder" at all, and smokeless has been used for a small arms propellant for at least 100 years longer.
Were aren't even close to the limit as far as what is presently capable in sabot polypropylene blends, or the quality of barrels that could (and should) be used in muzzleloaders. If you think there will be nothing further developed in muzzleloading propellants beyond Triple 7 in the next 17 years, we just could not disagree more. Morton Thiokol
already has done so, it is a matter of marketing focus.
As it is, several options exist today to cleanly harvest a deer at 200 yards-- yet, sub-100 yards are vast majority. A clean kill at the range you hunt is just that, the differences beyond that are just not particulary salient.