I just waded through the whole thread and noticed a few similarities with many of the posts.
We want a spydie fixed MBC to be thin and fast not a sharpened prybar.
It should be affordable ,no exotic expensive materials.
A lot of people mentioned sharpened back edges or double edges. I like a 1 third sharpened edge because it gives 95$ the advantages of a double edge but is much more useful. You could have the top edge spyderedged as an option.
Many people want a fixed Chinook and I concur. 5 to 7 inch blade with a sharp back third
A handle with a drop like on the Chinook3. I bet Keating could design a great fixed version.
In Vg10 this would be a very useful camp and kitchen knife with a thin edge and full height grind. Maybe make the back edge a little less than a third sharp so it would be more versatile.
In my opinion the best bowie style fighter is the Busse Pure Bred Fighter.

A fixed Chinook could be even better. A little wider blade and a bit more curve so it would be even sharper. A dropped and grippier handle ,the sharp back edge and a 100$ price tag and it would be the only knife like it on the market for even double or triple the price. Done right it would look classic.
Right now there is nothing closer than the Buck 119 which is the best unintended fighter under 100$ in my opinion.
About the FS dagger I have to disagree with Ken about the use of the flat spot. In the writings about how to hold it Sykes and Fairbain said to keep all your hand on the handle except with your thumb on the flat of the blade. I even read that the flat was there just for a place to put he logo. I think the best FS dagger was the blued second pattern which is why I bought exactly that one.
Here she is ,I love this knife. Her balance is superb and it feels more like a custom than wartime production.

The AF's and Case Devils Brigade daggers are no where close to the original. It is also very light to carry. Not at all useful as a utility tool.
Some of the original knives from Shanghai had the flat spot but most did not. They were also shorter than the FS.

Here is one of each.

This one makes me dizzy with lust. It has a beautiful ivory handle and a jap style habaki.
In case you have not guessed I like the FS Daggers and would love a quality repro.
No ringed handles ,steel not important ,might as well have a square shank.
I always thought a nice stacked leather handle would work well with the FS.