Thanks Resoman. Coincidentally I was reading the articles about David in AL56 today. So that article on bridge patches comes at a good time.
So the main things in that article are:
1) Bridge plates are important (more on this later);
2) Sound boards often split at the termination of bridges;
3) Bridges often terminate abruptly, and at the same point as patches;
4) Bridges and patches can form stress risers.
5) Properly designed bridge plates can eliminate SB cracks.
I would agree that soundboards crack for the reasons given, but I also think that instrument without carbon fiber, made in the modern way, are equally durable. The problem is not new, and the suggested prescriptions are only novel in their use of the material in question.
I also think that using the stiffest and strongest commonly available material as a patch can just as easily create a stress riser as using a bluntly ending bridge. As an example, lattice braced guitars, often have tops that fade out to the sides to a thickness of .5 mm. These are bolstered with a spiderweb of carbon, that is almost invisible. Not 30 thou of solid carbon.
These days there are other strategies, like scientific moisture control, spherical plates, better wood, less clunky bridge designs; etc... These also contribute to the split soundboard issue's resolution. And of course we don't know how long these plates and glues will last. For instance, if you put a plate of FRP with epoxy under a piece of wood, you are guaranteeing uneven absorption of moisture, in that area. That is a pretty good design for making one of those wooden moisture meters. So we are hoping that in 50 or 100 years, these will be the winning ideas. As the makers of instruments in the past assumed their choices would work out over time.
Getting back to 1), I am not convinced that these plates are necessary structurally, but do they produce better sounding instruments? Obviously people wouldn't use them if they killed the sound. Many older classicals didn't have them, and often used the fans to tie in to the bridge ends. But certainly the momentum has been towards under bridge plates. Some of the classicals that are using patches are using about 40 thou of softwood, so it doesn't take much to get a unified tone. Of course there is NA classical guitar making, and European guitar making. And there is the influence of steel string guitar making. I should probably get the whole book.
