Furthermore, despite how powerful RK healing is, they won't ever replace a minstrel or a beorning without competent raid support, however, a blue runekeeper could now spec into red for the +5% incoming damage buff and the -15% armour debuff (even more so because they can't be resisted anymore), that would make them quite valuable in cases where you wouldn't take a Red RK, but I don't think that alone is enough to warrant replacing a Minstrel for example.
The 5% damage has a 20% proc chance on every fire skill though, so keeping that up as a non-red RK means spending a large amount of time using fire skills. If that buff would be applied 100% of the time on a fire skill it would actually be meaningful for blue RK (and not change a thing for red, because red produces 100% uptime anyway)