At Las Vegas Fanfest Yoship mentioned common cross-skills are being changed in 4.0, each role will have minimum skills necessary for their job. Like tanks and provoke, so it's likely that protect/stoneskin will be available for all healers regardless.

I'd prefer they keep with the idea that White Mage does the most DPS of all the healers, along with superior AoE damage, and address the MP regeneration with more MP restore/instants like Assize, so that it's not behind Astro (it really shouldn't be, but Aether+CO is pretty darn good). Adding more mitigation is a grey-area, since it would step on the toes on the shielding healer. Astro gets a it's mitigation today to also make up for its lower dirunal regen potency.