Well I healed my first dungeon (Throne of the tides) and I'm going to share what I think is going to happen in cata (With the current talents/spells, etc...)

I think there are going to be 2 viable "specs", similar to how it is now with a holy light and flash of light spec.

Holy Light: I think any spec focusing on holy light is going to completely forget about intellect. That's right, no more intellect for holy light! I think holy light specs are going to stack spell power and haste. With the current mana cost, there is no need to have a large mana pool, and you will probably never run out of mana by just spamming holy light. This spec would be making full use of BoL, and holy shock may be used on cooldown because its basically mana neutral (If it crits you get more mana than it costs) and it heals for about as much as holy light.

Flash of Light: I think that a spec focusing on flash of light is going to continue stacking intellect, but gearing will be slightly different. Instead of the current situation where haste is basically better than any other stat (Crit or mp5), haste will become nearly useless for a flash of light spec. Crit will probably become the most important stat after intellect by far. Being able to crit more will not only help with the mana cost, but will play nicely with our new mastery bonus. Flash of Light specs should be able to provide huge AND quick heals while keeping their mana up just like we do now with Holy Light. So whats the downside? The lack of beacon being effective. This spec would more than likely be applying beacon with its new reduced mana cost, but it will not be used nearly as much. Since you should be able to throw a quick and huge heal at a tank it shouldn't be too much of an issue, and beacon will still apply to holy shock which will also be used on cooldown. The other benefit to this spec is the sacred shield HoT which is much stronger now that flash of light is much stronger.

If I had to guess, I would assume right now that the builds may look something like this:
Holy Light: http://cata.wowhead.com/talent#sxAVcxzVdMVqboxGzubhZV
Flash of Light: http://cata.wowhead.com/talent#sxAVcxzVdMVqboxZVfbx0h
The flash of light build focuses on increasing crit chance as much as possible, while the holy light build focuses on the utility that prot provides.

And as for divine light... I really see no use for it. Flash of light heals for a truck right now, and as stated in the article holy shock + flash of light can provide a ton of healing for a similar mana cost.