I'm not sure about your first idea, but as for healing spells damaging undead, it will probably never happen in FFXIV, simply because of how magic works here - here cure spells are not 'holy' elemental (which is why they damaged undead in past FF games), in fact, there is no 'holy' element in FFXIV at all (the closest to a holy-type element is the 'astral' aspect) - Cure is actually a water aspected spell, and also, the elemental wheel pretty much no longer exists in any really noticible way.

That and given how in FFXI the healing magic damaging undead trick was abused so much (especially when due to a bug people were doing 99999 damage to undead with Cure I), I think SE are pretty determined to avoid such problems here.