Well, I'd say we can pretty clearly pinpoint when cascading schemes makes sense: When we have different algs with different security properties and we can't hav

Well, I'd say we can pretty clearly pinpoint when cascading schemes makes sense: When we have different algs with different security properties and we can't have them all in one algorithm then cascading makes sense. This is the case for newhope + x25519, because one is based on well known crypto, but not quantum safe, the other is based on not so well known crypto, but (maybe) quantum safe. You could make similar arguments in the past about hash functions when the analysis around their safety was much more fuzzy. (Which is why I can also understand why Gentoo decided way back to combine sha2+whirlpool.)