the last frontier of MYOG?
For glue, if you are avoiding contact cement, including the 3M spray, instead maybe try Instant Krazy Glue® Wood and Leather
Salomon made some softshell shoes. Indestructability is way relative, seen by the number of people who use trail runners off the trail. They may not last for me, or Roger, but if you are talking about decent trails, careful travel, kayaking, or Hawaii, could be perfect.
I found the Paramo-Nikwax system interesting. Many people prefer no Gore-Tex in their boots, because it is such a barrier to drying! Plain leather has alot going for it, with the right water repellent. So you may not need industrial tech to make a desirable product.