If the player went through with the Dark Ritual to save their life at the end of Dragon Age: Origins, Kieran is the child of either the Warden, Loghain, or Alistair, and contains the soul of an old god, leading to his affectionate fan nickname, the OGB: Old God Baby. Inquisition hinted strongly that Kieran, or at least his soul, will have a big role to play in Dragon Age 4.
If Kieran is the OGB, his dialog is packed with unsettling omens. If The Inquisitor is a Dwarf, for example, OGB Kieran will comment that they “can’t be taller. Not without the titans,” perhaps hinting at the possibility that the titans will help create dwarven mages in Dragon Age 4. Similarly, an Elven Inquisitor will be noticed by OGB Kieran for their “old blood,” whereas a non-OGB Kieran will simply notice their big ears.
If Dragon Age: Origins' Warden went through with the Dark Ritual, Flemeth will take Kieran through Morrigan’s Eluvian and, when tracked down, gives Morrigan an ultimatum: keep Kieran and be pursued by Flemeth forever, or let Flemeth, revealed to be possessed by the goddess Mythal, keep Kieran. Morrigan chooses her son, but nonetheless Flemeth absorbs the soul of the old god Urthemiel from Kieran.
This seemingly wraps up Kieran’s story quite elegantly, as it means that Solas could theoretically have possession of Urthemiel’s soul in Dragon Age 4 (since Solas absorbed Flemeth) regardless of whether The Warden went through with the Dark Ritual. If the player didn't choose the Dark Ritual, it is entirely possible that Flemeth trapped Urthemiel's soul on her own. After all, it was Flemeth who taught Morrigan how to perform the ritual in the first place. However, Urthemiel's story is far from resolved.
Although Kieran is no longer the OGB, he may still be special. Depending on who his father is, Kieran could be the son of the King of Ferelden, he could be the first half-dwarf seen in the series, or he may have some lingering relationship to the Dark Ritual which means that, even without Urthemiel’s soul, he is still powerful.
Furthermore, Solas presumably now contains the power and souls of both Mythal and Urthemiel. Flemeth mentions a coming new era in both Dragon Age 2 and Inquisition, which could potentially be referring to the return of the Dread Wolf and the destruction of the Fade. Solas, as the dread wolf with these two new powers, could mean a lot of things for DA4. Flemeth’s ultimate motives have always been shrouded in mystery, as she helps the player stop the Blight in Dragon Age: Origins, and so clearly isn’t purely destructive. Solas, on the other hand, is a wild card.
It seems possible that the Dark Ritual from Dragon Age: Origins will have particular relevance in Dragon Age 4, Solas the Dread Wolf will have a number of plans to restore the old Elven world, and now has more power than any single entity seen thus far. What can be certain is that the world of Dragon Age is on the cusp of a new era one way or another. Urthemiel, Mythal, and the Dread Wolf will likely all have their own roles to play and motivations in mind, leaving it to the player to decide the ultimate outcome of the choice that started all the way back in Dragon Age: Origins.
Dragon Age 4 is in development.