Here are some firsthand experiences riding with a fully loaded bike in the mountains and the rain:

Rim brakes vary quite a bit in their stopping power and in their performance in wet conditions. Some of them have performed abysmally in the rain -- **much** worse than typically described -- and have given truly dangerously poor perfomance.

If any oil from the road (and the splashes and the rain) gets onto the already smooth braking surfaces, it is as if you have no brakes.

Ceramic rims are better; but the advantages are often overstated. They are better in the rain, but not overwhelmingly so -- maybe (rough estimate) 30% better.

They are said to be much better at not overheating. Again, I would say maybe 30% better.

They wear out brake pads much more quickly -- in my experience maybe three times as fast.

The rims themselves *do* last longer. Much longer. In this respect, they live up to the claims.

To me, they are worth it. I just replace pads more often and live with that. Jagwire and Pyramid have sold products that allow for the use of replaceable ceramic pads (that are usually used with V-brakes) with (smooth-post) cantilever brakes.

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Pulse braking has not worked so well (on steep, long, twisty, rough-gravel downhills that are impossible to ride safely at speed). Rims still overheated several times per run.

The method that worked best was taking it *very* slowly -- slower than walking speed. If riding a bit faster than walking speed, it still overheated the rims.

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Some kind of (rapid) rim cooling system might be possible. I have used water bottles, and they help. Very wet rags can also help cool the rims more quickly than air alone, especially when the air it is hot.