The quoted journald document promises:
breaking compatibility with existing standard and protocols, used not only by Linux systems, but by almost everything else,
coupling journald with systemd, thus making it non-portable, thus locking out non-Linux systems, all Linux systems not using systemd as an init replacement and most appliances,
using *undocumented* binary format for storing compressed and possibly encrypted and/or signed data.
Frankly, these three issues nullify all other described advantages.