I'd say its safe to assume that they'd have to depend on the DAC in the lightning-to-30 pin adapter to give them line-out. The question is, what DAC is Apple using in the adapter and is it subject to change as time progresses (i.e. they use a better or worse DAC in the future).
reading the apple site.
I don;t think there is a DAC in the convertor. Hence no support for Line-Out OR video out which means it is a pure Digital Signal.
Will need an external DAC of sort.