it could be argued that most cpus are 4 to 8 core now, and that speed doesn't really matter - and in that instance there are other alternatives too like zhuff:
which is by the same author as lz4. the cool thing about lz4 is it's not really slower than doing no compression at all, and on space starved ssd's etc, it could become a happy default.
when the next generation of ssd's come it should be a bit more obvious. on ssd raid it's already obvious when copying files over fast network connections. but i realise most people only have gigabit atm.
the main thing is it's pending for ages, and it seems to have somehow missed being included. it'll also need to be included in grub support etc to be applicable to most users, and being included in mainstream is going to make that a lot easier. in zfs it's easy to see it outperforming lzjb but lzo isn't lzjb.
for some reason btrfs on systems i've tried it on often seem to lag on disk writes afterwards with high cpu usage. i don't know if it's compression or normal background activities, but it's quite noticably intrusive enough so that on my main server i'm using ext4 on raid for /, and zfs for data.