It was confirmed last week that the change will occur in Patch 2.3 and the extra Spell Damage will equal 1/3 of the +Healing stat on gear. So, for example, an item with +75 Healing will have +25 Spell Damage added to it without reducing any other stats.
Some confusion has occurred, however, about just how generous Blizzard was going to be with the free Spell Damage. Forum poster Bridge requested a link to prove that "this includes enchants, gems and set bonuses".
Drysc stepped up to the challenge:
It includes enchants, gems, and all other items. The only exceptions are temporary buffs, and some BC leveling greens with "of the..." stats, and some Zul'Gurub items, as there is a current limitation on how many different stats can be distributed on an item, which we're working to extend for the future.
It seems Blizzard is going to be very generous indeed: +Healing enchants and gem bonuses will now include Spell Damage.
It is unfortunate that some items have programming limitations so that the +Spell Damage stat cannot be added because there are too many stats already. There is no time frame indicated as to when the maximum number of stats on an item will be increased.
This is one of the changes I'm really looking forward to in 2.3. Specing and gearing for Restoration or Holy will no longer mean you are gimped whenever you're not healing.
I think that with so much Spell Damage being added to healer gear, there will be a greater availability of healers for groups. What do you think?