Moving will be made to interrupt spellcasting at a point in time...

[Rowyne]

I hope Yoshi-P has more of a game plan than "No movement while casting"... maybe something to alleviate it, but that's a really far stretch. I guess his approach is "Good positioning for party members", like in Ifrit Battle.

I don't think it's a great concept for playing on an open field.

Usually in games where players are more on the move, healers are given instant cast HoT (heal over time) spells that can be cast while moving to keep people topped off. That lets parties continue to be on the move through dungeons and open fields, and gives healers a little wiggle room in a boss fight if they need to move suddenly.

While we currently don't have anything like this, that may change in 2.0.

Additionally, according to the class reform list, White Mage will be getting two abilities that will allow for instant cast heals. One will eliminate the cast time of the next spell, the second instantly restores HP of all party members.