Hypothetically speaking, if one were to Gestalt DfA and Warlock, how would invocations work? Both have some overlap but the lists are fairly different. Obviously Blast essences and shapes are replaced by Breath Effects for the DfA, but the Warlock has a much larger list of general invocations, and the effective amount you get is different between the two. Also, Breath Effects only apply to DfA, and Blast Shape/Essence only apply to Warlock's EB, but are still counted against their known invocations.
The major difference between the two, if gestalted with other classes, is that the DfA's breath weapon is a supernatural effect, and could, for instance, be used while in a Barbarian's Rage, while eldritch blast could not.
Am still looking at different synergistic combos, anyway.