Combining hash functions is actually trickier than it looks, and some people are doing research in this area and deploying solutions. See https://crypto.stackexchange.com/a/328 and https://tahoe-lafs.org/trac/tahoe-lafs/wiki/OneHundredYearCryptography. It does seem that if cryptography people had more of a security mindset (that are not being defeated) then there would be more research and deployment of this already.
Combining hash functions is actually trickier than it looks, and some people are doing research in this area and deploying solutions. See https://crypto.stackexchange.com/a/328 and https://tahoe-lafs.org/trac/tahoe-lafs/wiki/OneHundredYearCryptography. It does seem that if cryptography people had more of a security mindset (that are not being defeated) then there would be more research and deployment of this already.