Well, I've said it before, I'll say it again.
A 1/3rd sheath like that is going to fall apart, the design is not even remotely close to the simple durability of a wood and leather one-piece scabbard.
Its going to get rainwater running down the blade (especially a fullered blade) and collecting in the bottom of the sheath, damaging the blade. As it would be medieval leather, it would have to be vegetanned leather, not a chrome-tan - an entirely modern process. That contains tannins, which will chemically react with iron/steel, making the blade get stained black in areas it touched. if the leather's wet, it will corrode the steel significantly; active rusting. If the weather wet it will also deform and warp, because there's no underlying structure to it, like a proper scabbard.
Because its an all-leather construction, there's no support for the bottom of the sheath, meaning when its drawn, it flops all over the place. Due to the length, that's going to end up tangling between the user's legs, getting in the way. That's a common problem that reenactors who use soft leather sheaths, instead of rigid wooden-cored scabbards, by the way. And that's very much also something you really don't want in a real fight when your life's at stake. You also dont want something that's attached over your shoulder with great big hooks on it that are screaming "use me as a grappling point" to your opponent, who can use the stuff you're wearing to your disadvantage.
Then there's the whole space issue. to draw over the shoulder means you're going to have to turn the blade at shoulder height. lets say for simplicity, you're 1m 80, and the sword blade is 1.10m long, with a 40cm hilt Well, I just did a quick check with a 14th C longsword that's got a 97cm blade... and I hit the 2.5m high ceiling. If you're in a rush, you need to easily have a 3m ceiling height to practically draw over the shoulder (plus a metre of clear space behind you), or you're going to be hitting the roof. Now ingame we might not have a ceiling, but I cant really envisage the gloomy dungeons of SG and Exanima are blessed with high, bright airy ceilings in every corridor...
Outdoors it would be fine. But guess what? Outdoors, you can use a normal scabbard, and carry it on your horse.
When drawn, it will also lose rigidity, meaning it makes it utterly impractical to sheath. Unless you're wanting to play "stab myself in the back of the leg" while poking around blindly like a drunken virgin, you're left having to unstrap the thing, turn it round so its facing your front, use both hands, one holding your sword, the other the scabbard and thread the tip into the gap for the bottom part of the sheath, then line up the top, notch it over these two oversized hooks, and secure it. then take the assembly, sling it over the shoulder, and tighten up the baldric so you dont have it slip.
Or... you just prop it on your shoulder. Hmm. I wonder which is more practical?
And, all, meanwhile, while the contraption fails to provide any actual protection for the edge of the weapon, or protection from the elements - the two most important elements of the purpose of a scabbard. In this regard, its about as much use as a chocolate teapot.
That's what I mean that it wont work.
Its not about applying a historical setting to a fantasy world, its about the fact that if things are being used, they have to actually do the job. and those scabbards simply dont work. (Aside from the aesthetic horrors of tartan-clad renfair cockwombles). If it works in a historically plausible manner, that's just a bonus for my tastes.
This is for a game were talking about here. You know that right? Whats the point of playing a low fantasy game if everything is going to be so realistic you cant have fun? Ill stick to real life if games become so realistic they get boring.
I appreciate your passion though. Its amazing man. Do you make these or something? I would love to see some of your work if so.