Alright, I've been thinking about this awhile, and here's what I'm poking at so far:
Light/Dark will be shifted to mostly be made up of the following types of spells:
1) "Smite" spells
2) "Miracles" (more on these further in)
3) Miens
4) Each element's "flavor" damage spells
5) Status effect appliers (Weigh Sin, Hex, etc.)
So, let's talk about each:
"Smite" spells: These are new. Light and Dark will each be getting two: one is a straight up, no cooldown, but low power/moderate SP cost direct smite. The other has a Light or Dark (as appropriate) cooldown of 1 turn, but amps up the power. Why bother with a 1 turn cooldown? Well...
"Miracle" spells: These are also new...well, newish. They will resemble the old style smites, except they all have the distinction of affecting every enemy in a wide area who meets the condition. Almost every word of that is key: they only affect enemies, and they affect all of them you can see, except for those at the *very* edge of LoS (for FerretDev reasons, most hostile abilities are never allowed to hit things at the extreme edge of LoS, and these will be no exception.) So, for example, Humble will affect *every* enemy at > 50% HP now. Additionally, you will find these have low or no SP cost... but their cooldowns are significantly higher, probably somewhere around 6 or so. (This is when it starts to matter which "Smites" you're running with: the low power, no cooldown one is always usable, but the high power one gets shut down once you use a miracle.) Miracles will probably be highish power: 85 is the most likely candidate, which is usually the maximum for AEs that can't miss (Breath Weapon + Tireless is one of the few ways around this.) Keep in mind that even a Jinn's Fireball is only 55 Power... and 85 Power is what a full power breath weapon (without Tireless) hits at: 85 is pretty heavy.
Miens: These will pretty much be unchanged in concept, though the specifics will likely change in some cases: basically the idea is that they add extra effects to Light/Dark damage spells if extra conditions are met. Interesting combinations abound with all 3 of the types of damage spells available: With Smites, you can potentially trigger the effect on individual targets while waiting for a good time to throw a miracle. With Miracles, you can potentially trigger the effect on multiple targets at once.
"Flavor" damage spells: Essentially, things like Light Dart, Wraith Touch, Vigor Siphon. In essence, Light gets "friendly" projectiles that allow you the option of spending points on Agility (or finding other ways to get accuracy) to get what effectively act like even higher Power smites with no cooldowns. Dark will continue to get MaxHP draining as before. Not really any changes here per se, but the changes to miens will likely have some effects here. I will probably add Light Arrow in order to even things out (85 Power, higher SP cost version of Light Dart) You can also include things like Holy Word (the Light-elemental breath weapon) in here as well, little one-offs that were added for... well, flavor.
Status appliers: No real changes here, but it's worth pointing out a difference in how Light/Dark handle these versus say, Debuff. The single target versions tend to be equally straightforward, but Light/Dark status appliers hit all enemies, where as Debuff targets an area indiscriminately.
The basic goals are:
1) Make them both more fun/usable in general. Both will have a fair number of spells that are generally useful and usable even when the cooldown is active, giving you good things to do while you set up for a miracle
2) Big payoff from Miracles/Miens: Getting things set up right for a miracle will be tough, but the payoff should be quite nice when it works, especially if match up some miens too.
3) Reward deep investment in Light/Dark: The Miens were intended to start this, but I'll try to find some other new passives too. We'll see what I come up with. Of course, there is the issue of resists/immunities to concern yourself with, so I'm not expecting anyone to ever go 7-8 Light or 7-8 Dark, but it'd be nice if there were solid reasons to play a 5-6 of one build.
4) Interesting build options from Miens, for both heavy Light/Dark users, and for those dabbling in it: I like what Reaper's Mien has done for Dark usability, I'm hoping I can get more of them to that level.
Anyway, that's where I'm at on this for the moment. This will probably be the major "thing" in the first "resting hamster" build. Feel free to chime in with any thoughts, comments, suggestions, etc.