Right now, next to nothing is known about Dragon Age 4 except for what Inquisition makes clear. Solas will return, the next game is likely set in Tevinter, and several conflicts that have plagued Thedas seemed to be colliding. Furthermore, it's obvious based on the Temple of Mythal, the Ancient Elves, and what Dorian learns of Tevinter that many things that fans have assumed to be true may not be such.
One example is how history teaches that Tevinter destroyed Arlathan and the Ancient Elves, but that's proven false in a lot of ways. Another seemingly misconceived notion is that Tevinter Magisters like Corypheus blackened the Golden City, but that too is seemingly untrue, as they state it was already black and the throne was empty upon arrival. Dragon Age 4 fans will likely have a lot of questions answered, but one major one involves the Darkspawn Civil War in Dragon Age: Origins - Awakening.
Darkspawn Civil War
The Darkspawn Civil War is the main focus of Dragon Age: Origins - Awakening, where players take on the role of their Warden again or a new Warden Commander if they made the Ultimate Sacrifice. In it, they discover the Architect has a way of "awakening" fellow Darkspawn, restoring or giving them a new level of intelligence but also fracturing the Darkspawn post-Blight. The Architect's followers and the Mother's followers are at war, with the player putting an end to the Mother scheme's during the Assault of Amaranthine/Siege of Vigil's Keep questline.
However, what players do with The Architect is left up to them entirely, as they soon learn that the awakening process requires Grey Warden blood and that The Architect started the Blight when trying to awaken Urethemiel. Players choose whether or not to kill the Architect, which has little bearing afterward. If the Warden is the same as Origins, then in Inquisition, it's mentioned that they are on a quest to end the Calling, something likely related to the Darkspawn Civil War. In other words, ending the Calling and preventing future blights may all be tied back to this Civil War.
Dragon Age 4, The Warden, and The Calling
But what this means further is that the Darkspawn are not necessarily vile, despicable creatures. The Warden blood gives them immunity to the taint and the Old Gods, meaning under all of that, there still retains some form of humanity. After all, a Broodmother is created by a captured Thedas race (Human, Elf, Dwarf, or Qunari) and are used to breed thousands of a specific Darkspawn race - Hurlocks, Shrieks, Genlocks, and Ogres.
Darkspawn are not inherently evil, just tainted, as proved by the Architect. This means ending the calling, ending the call of the Old Gods, and purifying the taint may restore more than just intelligence. Of course, this is up in the air but would make an excellent subplot to develop through a Darkspawn companion in Dragon Age 4.
This also means the Warden's quest may be more important than first meets the eye, as while Solas' plan may be focused on bringing his ideal Elven Society back, there's a good chance that that's more connected to the blight. After all, many think the Veil was always there with the Maker on the other side; Solas proves this isn't true. Tevinter Magisters, according to Corypheus, were called by the Old Gods to cross the Veil, but why and how would they do that if they were underground at the time of the Darkspawn's creation (as they found Dumat and corrupted him then). The Dwarves have no origin story for the Darkspawn, despite living in the Deep Roads their entire life, and that factor in for DA4 as well.
In short, the Evanuris elven Gods, the old Gods of Tevinter, the Blight, and the Darkspawn are all so connected that resolving the first through Solas's villainous actions suggest that the latter be resolved too. The Warden is involved somehow and all signs point toward some major revelations in Dragon Age 4.
And that's not even factoring in the Dwarven magic, the Titans of their lore, or how lyrium connects the Deep Roads to the plot as well. For now, fans just need to wait and see what BioWare has up its sleeves.
Dragon Age 4 is in development.