After taking a look at it, Eldritch Disciple can easily be adapted to Dragonfire Adept/Cleric very easily, by simply changing the flavor text. All the abilities seem to match up. Essentially, Dragonfire Adept is just the Warlock only it doesn't need to bother with ranged touch attacks, has poor BAB (which doesn't affect your breath weapon), better HD, fewer invocations, but access to Breath . What I don't know about is the power level. Also, Eldritch Disciple doesn't advance eldritch blast/breath weapon damage, so that would limit you there as well.
I started writing it up on the plane coming home. ED does advance Eldritch Blast, as it's technically an invocation (and called out as being advanced). My adaptation specifically advances breath weapon, and has a slightly different set of abilities to chose from.
Here's what I have so far. It's mostly a direct rip from ED:
[spoiler]
Dragonfire Disciple:Prereqs: 2nd level divine spells
Ability to use least invocations
Knowledge (Religion) 8 ranks
Knowledge (Arcana) 4 ranks
Ability to turn or rebuke undead, dragons, or creatures with an elemental subtype.
Dragonblood subtype
BAB: Med
Good Saves: Fort, Will
Hit Die: D8
Class Skills (2 + Int modifier per level): Appraise, Bluff, Concentration, Craft, Decipher Script, Diplomacy, Intimidate, Knowledge (arcana), Knowledge (nature), Knowledge (religion), Knowledge (the planes), Listen, Sense Motive, Spellcraft, Spot.
Invocations: At each level, you gain new invocations known and an increase in caster level as if you had also gained a level in an invocation-using class to which you belonged before adding the prestige class level. You do not, however, gain any other benefit a character of that class would have gained. If you had more than one invocation-using class before becoming an eldritch disciple, you must decide to which class to add each level for the purpose of determining caster level and invocations known.
Spellcasting: At each level beyond 1st, you gain new spells per day and an increase in caster level (and spells known, if applicable) as if you had also gained a level in a divine spellcasting class to which you belonged before adding the prestige class level. You do not, however, gain any other benefit a character of that class would have gained. If you had more than one divine spellcasting class before becoming an eldritch disciple, you must decide to which class to add each level for the purpose of determining spells per day, caster level, and spells known.
Turn/Rebuke Undead: Your eldritch disciple level stacks with your other class levels for the purpose of determining your ability to turn or rebuke undead.
Breath Weapon: If you have a breath weapon with level-dependant effects (such as from the Dragonfire adept class), levels in Draconic Disciple stack with levels in the class that grants that ability for determining damage, range, or any other effect that varies by level. If you do not have a Breath Weapon with level-dependant effects, this class feature has no effect.
Dragonfire Channeling: At 1st level, you deepen the connection to the raw arcane magic of Dragonkind. Choose one of the following abilities at 1st level, and another ability every three levels thereafter (4th, 7th, and 10th level). You can spend one of your turn/rebuke attempts as a swift action to activate the chosen power.
Damage Reduction: You gain temporary damage reduction (overcome by magic) equal to your class level (minimum 1).This damage reduction stacks with the damage reduction granted by the dragonfire adept class. This effect lasts for a number of rounds equal to 3 + your Cha modifier (minimum
1 round).
Healing Breath: You can change your Breath Weapon into a healing breath. The breath heals living creatures instead of dealing damage to them (the damage healed is equal to the damage normally
dealt). Against undead, the healing breath deals damage as normal; against constructs or objects, the healing breath has no effect.
Energy Resistance: You gain resistance to two energy types equal to 10 + your class level. Choose the two energy types when selecting this ability. If you have the Draconic Heritage feat for a dragon that has an energy type associated with it, one of your choices must be that energy type. Once you choose the energy types, you may not change your choices. This effect lasts for a number of rounds equal to 3 + your Cha modifier.
Energy Substitution: Choose one energy type, other than fire. If you have the Draconic Heritage feat for a dragon that has an energy type associated with it, you must choose that energy type. Once you choose the energy type, you may not change your choice. Breath weapon can do this energy type instead of fire. Unlike other dragonfire channeling abilities, this ability does not cost turn or rebuke attempts to activate. You may choose when breathing which energy type to use.
Frightful Presence: You can render a single living creature within 30 feet of you shaken for 1 round (Will negates; DC 10 + class level + Cha modifier). The creature's HD can't exceed your character level.
Draconic Senses: You sharpen your senses, gaining a bonus equal to 1/2 your class level (rounded down) on Listen, Spot, and Search checks. This effect lasts for a number of rounds equal to 3 + your Cha modifier.[/spoiler]
It still needs something to replace Eldritch Spellweave, and a capstone ability, and maybe a Dragonfire Channeling ability having to do with knowledges, since that would be very useful to my character. I should probably put this up on the homebrew forum....
DfA least invocation Draconic Knowledge is great- +6 to all knowledge skills, which as cloistered cleric you have as class skills anyway.
This is exactly what got me thinking about DfA in the first place. That goes a long way towards making Knowledge devotion kick even more ass. It also frees up having to put a point in all the skills, since it allows you to make knowledge checks untrained.