That one's only a little bad if you do it - you break uncompressed ARC with compressed L2ARC, nopwrite, and dedup, but all three of those are uncommon cases, an

That one's only a little bad if you do it - you break uncompressed ARC with compressed L2ARC, nopwrite, and dedup, but all three of those are uncommon cases, and you can add helpful glue to make it work without breaking those with only a little work. For example, we've had three different zlibs compressing gzip streams for a while, and nobody really complained about it. (Linux ships 1.1.x; FBSD and everyone else ships 1.2.x; Intel QAT produces identical output to neither.) For a while, zstd was outputting different results on BE and LE systems and nobody noticed. Most of the reason we haven't updated compressors nowadays is that nobody's convinced anyone it's got enough benefit to be worth the added complexity.