I like that you're going out on a limb to update the divine disciple tree, and I think it seems fairly good, but I'd like to please suggest some further updates.
Cleric domains brought a lot of life back into the class, but there are only a small few which players find useful to take. Some are less than ideal. I'll use water domain as an example.
Water domain gets a couple of nice SLA's, some bonus SP, and SP<->SP conversion, but there is nothing in any cleric enhancement tree to reinforce that faith choice, it's healing, melee, or light/fire/negative caster. From a casters gameplay perspective it is just better to just sound burst+firestorm/holy smite/celestial bombardment/etc.
I would like to suggest that the DD tree pull from the cleric domains which the player has chosen, rather to be narrowly confined to light & negative. We already have a quite light focused tree (AoV), so making better use of all the domains should make for a better player experience.
There could be sla's in the tiers:
- water domain might get niacs at t2, snowball storm at t4, ottilukes at t5
- knowledge domain might get detect secret doors at t2, nothing is hidden at t4, trapfinding at t5 (maybe using a skill conversion)
- strength domain might get rams might at t2, roc's strength at t4, and titan's grip at t5
and so on. These are just rough ideas.
I think that the domain should also get access to elemental bypass for spells of that domain, as part of the capstone. This would help to put them in line with other offensive casters, and to help mitigate the current divine caster meta of only going with light & force spells (because nothing is immune) & Tiefling & fire spells (because that lets you bypass immunity).
Because the various Master of <> feats do not currently encompass most of the potential spells of this idea, I think that DD should grant bonus MCL to spells & sla's of their domain as part of the cores. I don't think there should be bonus caster levels as without them it would the opportunity cost to stay pure vs multiclass.
Would it be difficult to pull from domain feat selections? Maybe having a multi-selector a la Half Elf Dilettante or kensai weapon enhancements?
Hope you see this. Cheers.