Ykurtz, kangaroo leather for a riding jacket sounds like the bomb! Who makes one? Kangaroo is supposed to be the best abrasion resistant leather. My Held racing gloves have kangaroo on the palms.
I think that Kushitani amongst others makes Roo gear. I've got a pair of their gloves that were about $250. Super light, but tough as I discovered twice on the tarmac. I'm sure others make it too.
Been fortunate to have accumulated jackets made from goat (langlitz) and others, naked cow (Schott), horsehide (several makers), bison (Aero) and steer hide. Also a few in sheep hide including two b3's. Living in Oregon, these all have been wet, to the point of soaking wet. Would like to have one of the b3's shrink a bit, but never did. Not brave? enough to put it in a dryer! Only one I worried about was the Schott naked cow. Use mink oil in paste form once a year or so to keep it conditioned. Other jackets are from 35+ years old to about 6 years old from a recent purchase. Pecards, langlitz, lexol, and or mink oil help protect them. No shrinkage in the naked cowhide, just towel dry and hang it on the back of a chair to dry. I think the mink oil did darken the cow hide a small amount, but still looks good. Maybe lucky with the cowhide!
As a regular rider, riding in the rain is an occupational hazard you could say as I live in England. I have worn bike specific gear and none has shrunk from getting wet, also various other jackets from Aero/ Eastman plus many other producers have also taken a good pounding in our sometimes unpredictable weather. One of the big problems is drying out your sodden clothing. Never hang it next to or above a radiator or in any really warm tempting drying area. That is where shrinkage will really happen. Sometimes even after a rainstorm on a hot day, hanging in the sun could affect this as summer heat can be detrimental unless you are out riding of course. The best way is to let the clothing dry out in a normal warm room, not much more than a normal room temperature and you should be ok. Just my experiences with wet leather under motorcycling conditions.