There is ways to continue Dark Dawn's plot, it's actually rather easy.
First, DD's main plot is done, the grave eclipse is settled. We just need to have it summarized just like the event of the first to games during the opening. or even better, have it happen during the prologue.
Then, follow new characters. Probably not knowing how the eclipse happened, so new players won't know, just like characters, but we, old players, will know, and that can lead to interresting bread crumming and subtle story telling. Make the first part of the game about understanding what happened, maybe because it had a lasting effect on a character (once again I bring the idea of one of the character being "infected"/"changed" by dark psynergy, not making them berserk just them having powers they don't understand and may be afraid of, and now are looking for a cure/explanation.
That first part of the game would allow to introduce the lore, the recent events and important characters slowly, by learning what have happened. "Oh, children of the warrior of Vale were tied to that eclipse." etc etc, until you find them, maybe even finding them right were DD ends, when they are in front of the big vortex.
Eh, maybe the character affect by dark psynergy actually has the ability to control, or at least tame down vortexes.
So you see it's not that hard.
