It seems to me that the Knight Disk and the CVA Buckhorn are basically a copy of the Remington 700 ML design; which means a modern rifle design adapted to muzzleloading. All three have a nearly useless bolt....it don't lock the breech, it don't feed, and it don't extract. All it does is move the firing pin behind the cap....and make the rifle longer than it needs to be. The Knight disc is still my favorite because the quality seems to be high, but I don't really see any innovation there. I think the break action guns will win out in the end.....when they finally make one that's not junk.
They allow easier access to the cap and don't add length to the rifle.
In fact, if a side-lock rifle had a breech plug (a major convenience) there wouldn't be a huge advantage to an inline anyway. In my humble opinion.
