I would want this to be toggled on/off, because I don’t want to always have it visible (eg. in a crowded dungeon I want to be concentrating on my own HP more than the morons who are going too deep around me).
Or have a further setting to make it display for locklist/friend allies only.
The over-your-head indicator might be of interest to other heal classes (necro/pala), or even just as a global option. That warrior might want to know that his allies are struggling so could back out to assist clear whatever is destroying them.
It sounds like they’re planning some change to the HP bars so maybe that will be a benefit to helpful priests if the colour is more noticeable. Going off on a tangent, having HP bars option being a 4-way choice (all, enemies-only, players-only, none) would be useful too.