As long as it’s loaded thru the muzzle, who cares? That by definition is a muzzleloader.
That's about how I feel. People that know me may be surprised, but I have absolutely nothing against modern designs. I own a few modern 209 primer muzzleloaders. What's different for me than other people is that I genuinely love muzzleloaders, and the history of firearms. Since I also love hunting, it is only natural that I hunt with muzzleloaders. It shouldn't be a huge surprise that firearms built in the 1700's and early 1800's, the prime years of muzzleloaders were built to be used. Their designs are the most fun to me to shoot and hunt with, that's what they were built to do.
Some people have this idea that scopes, inline ignition muzzleloaders, and bullets are modern 20th century or newer ideas, and they aren't true. Inline designs are rare, but they existed. Rifle scopes existed even in the 18th century, although they didn't really get use until the 19th century. They just were not used much for hunters. Bullets, meaning elongated projectiles, especially are not a modern idea. They weren't used very much since they didn't offer that much advantage to the average person. They weighed more, they didn't kill any better, and I suspect accuracy was not that great. Rifles built back then were hand made and even the barrels were made using machines more akin to jigs than lathes. Barrel dimensions varied rifle to rifle. Bullet molds, almost always a basic round ball, were sold with each individual rifle so they could fit properly. Different parts of the world did things differently. Here in the new USA we embraced cloth patch around a round ball as the gold standard for accuracy. Generally linen was the standard cloth then. This patch cleaned the bore slightly when loading, and provided a good fit for the ball for accuracy. A patch is by definition, a sabot for a round ball. There's nothing that says a sabot is plastic. Wood and leather are other materials used traditionally for sabots.
So to get to the point, my opinion on what laws should be for todays muzzleloading hunting season really comes down to the intention of the season more than being historically correct. In my opinion the muzzleloader season should allow a hunter some advantages over the standard firearms season to give them a fair chance at a good animal with a supposedly more difficult firearm to use. The most distinct examples I can think of in my area is the MN and SD muzzleloader seasons. In MN their muzzleloader season is extremely short, only a couple weeks, and it starts right after their regular firearms season. By every metric, the MN muzzleloader season is much harder than the regular firearms season. It's become nothing more than an extra couple weeks firearms hunters use to fill the freezer, it isn't an honest muzzleloader season.
By comparison SD muzzleloader season has a HUGE advantage right off the bat. Most firearms tags here are only valid in a single county. The muzzleloader tag is valid state wide. On top of that the season is a full month long. It is after the firearms season, but it is long enough most deer can settle down a little. This is an honest muzzleloader season.
I don't like weird restrictions myself. States like Idaho made restrictions with good intentions, but all people did was skirt the law with design changes. I'm ok with the ban on 209 primers, but at the same time they don't really give anyone an advantage. Whether its ignited by percussion cap, musket cap, 209 primer, or other, if it goes bang, it goes bang. At least they allow double barrels. SXS's are traditional dating way back. Some states don't allow them, which is outright stupid. Idaho only allows loose powder. I only shoot loose powder, but that's because it's better. Pellets and sticks are what they are. They aren't as accurate, and they cost way more. I wouldn't support this regulation. What I would support is that everything must be loaded from the muzzle. This seems so obvious to me, but apparently not to others. While cartridge guns did exist way back, this isn't the historical season, this is the MUZZLELOADER season. Everything in your barrel, powder, wads, projectile, etc. must be loaded from the muzzle end, no exceptions. This is one of the few areas I draw a hard line. Those Federal fire sticks are the dumbest thing I've ever seen. That's a straight up cartridge you load in the rear. It's not even subtle, it's a middle finger to everyone who likes muzzleloaders. I see no difference between that and allowing BPCR's. Having a separate "traditional" season with those is for another discussion.
Back to picking on Idaho, but applies to most western states is the open ignition regulations. Idaho says your "cap", meaning any ignition type, is clearly exposed and visible with the hammer cocked. This is one of those regulations with good intentions with terrible outcomes. Now there's all kinds of "western legal" abominations out there that exist for no reason but to skirt regulations. I have no problem with people using these rifles, but I also think the regulation is stupid. If you are using a modern inline rifle, what difference does it make if you can see the primer? It's the same rifle, except one has a cutout or hole.
One other quick Idaho example is the "projectile must be within .010" of bore diameter". Presumably to allow patched round ball, but not allow plastic sabots. In one of my 54 caliber rifles, .540" bore, I shoot a thick patch and .520" ball. So that's not legal in Idaho? Another regulation with good intention, but poor execution.
Lastly is the scope issue. I think most view scopes as a huge advantage, and in certain instances they could be. They are also a part of muzzleloader history. I think most of us know when people are pushing it too far. If you are out there with a $1500 rifle that looks like a Remington 700 and 4-12x Leupold scope on it, you are probably in the wrong season. I also don't see anything wrong with people who want to use scopes, to use scopes. Especially as people get older, a 2x scope can be a godsend for those with less than ideal eyes.
If I were to write regulations for my state big game muzzleloader season, it might look like the following.
December 1-31
minimum caliber 40
handguns, minimum caliber 44 (I'm fine with cap and ball revolvers)
must be loaded from the muzzle only
open or aperture sights permitted
fixed power scope permitted (seems a good compromise, and more historically correct)
That's about all I'd have. Some like to choose things for others. I trust fellow hunters will make the right choices and not shoot a 40 caliber PRB at an elk.