I have has some experience with the repairability of a V-joint. One of my customers was teaching a beginners class, and one young lady had a guitar that had such high action she couldn't play it. He traded for the duration of the class, and told her to come in early next time so he could fix her instrument. At the end, while he was erasing the blackboard, she stood his guitar on a chair and left. He heard it start to fall, but was too late. He set a chair over the wreckage, finished cleaning up, and swept it into the case without looking too closely. The next morning he was at my door when I opened.
The break was 100% along the glue line. Hide glue, although strong in normal loading, has very low shock resistance. When the back of the headstock hit the floor the glue simply broke, taking no wood along with it. It was a simple matter to wash it off with warm water, and reglue it. He was out of the shop two hours later, with the admonition not to string it up for at least six more hours. That was about ten years ago, and he says he is seldom more than 10 feet from that guitar.
At this point, on a good day, I can cut a V-join in about 1/2 hour. On a bad day it takes more like 2 hours. I find there is a strong correlation betwen how good the day is and how sharp my chisels are. Hmmmm.
The so-called 'Fusen V-joint' that Hauser used is a modified bridle joint. It is very hard to disassemble, and when stressed I fear would always break wood. It is actually a fairly easy joint to cut and fit if you have a table saw, and I imagine some clever jigging would make it easy enough with hand tools.
The scarf joint works well, but perhaps better with synthetic than hide glue. The synthetics are more flexible, thus tougher and more shock resistant. I have seen scarfs that have come entirely unglued, with the head held on only by the face veneers. Once they start to peel up, these glues just keep going. Sadly, the modern glues are harder to repair well, since they don't 'burn in'; new aliphatic resin glue does not stick very well to old glue.
I often feel that all of the traditional Spanish methods make a lot of sense if you keep in mind that wood was expensive and labor relatively cheap. They would go to some lengths to use a little less wood.