Next to nothing is known about Dragon Age 4, not even its proper title, and there's a few reasons behind that. Previous reports indicate that Dragon Age Joplin Project (its code name) was cancelled and would've seen players take on the roles of Spies in the Tevinter Imperium. The project in development now, Morrison, may use some of that or may use none of that, but there's a few good hints looking at past DA games when it comes to what to expect.
The game is going to take place in Tevinter; there's been too many teases and too much history with Elves for it not to. There'll be a new protagonist, with perhaps previous protagonists playing a background role if not an in-game role. And there's sure to be the return of a franchise staple: Dragon Age's romance system. It has evolved over the years, but there's one thing fans have clamored to do but has not: romance a dwarf.
The most logical explanation is the game's mechanical limitations, despite the fact that those who play Dwarves can still take part of many romances. Another possibility is that Dwarven companions thus far have been unavailable, but whatever the reason, there's a history that can be looked at to suggest that not only should its romance system continue to evolve but Dwarves be included too.
Dragon Age: Origins
Hearkening back to 2009's Dragon Age: Origins, players see the romance system in its most rudiment form. Players could romance either Morrigan, Leliana, Zevran, or Alistair, while this quickly devolved into a gift-giving into the heart style of gameplay with DLC. Basic personal quests were involved but overall it was not that deep. Plenty of people loved Oghren, he even considered himself single, but he also still falls into the unavailable category. The situation with Branka, however it plays out, is reasonably too much for his heart.
Notably, while these basic romances see limited influence (outside of Morrigan and the OGB Ritual, of course), they matter more as the franchise goes on. Each, in some regard, talk about the Warden or vice-versa in future entries, all dependent on player choice.
Dragon Age 2
Dragon Age 2's resident dwarf, most recently seen in Dragon Age: Inquisition, is perhaps the characters fans want to romance the most but have never been able too. Having been a companion in two games now, it's clear that Varric's history goes further back, as players finally meet and understand Varric and Bianca's relationship. As such, it's unlikely that Varric will ever change, but that's not to say Dragon Age 2 didn't get some things right.
For example, many of the romances reacted moreso to the events of the story in Dragon Age 2 than in Origins, such as when Hawke's mother is murdered or when it turns out that Isabela's relationship with the Qun is strained. It, despite its flaws, set a foundation and pushed romance options forward, even if Varric wasn't part of that.
Dragon Age: Inquisition
Dragon Age: Inquisition has 8 total official romances: Blackwall (female only), Cassandra Pentaghast (male only), Cullen (female human and elf only), Dorian (male only), Iron Bull (male and female), Josephine (male and female), Sera (female), and Solas (female elf only). The diversity introduced here meant that any single Inquisitor only had 4-5 options, and each of these romances felt unique. Solas' restrictions are made abundantly clear as to why, and those who favor the him had their hearts broken. Dorian's was heartfelt, Iron Bull's was mostly physical and dependent upon choices as to how it turns out by Trespasser, and Cullen's was everything fans wanted.
And Inquisition did, in a way, cater to fan desires here. Although not much would ever manifest from it, aside from learning her first name is Lace, players could flirt with Scout Harding. This shows Dwarven romances were considered, touched upon, but never expounded with. It's unsure why, and for those who want this romance option, it was a bit of a double-edged sword to know the flirting would go nowhere. However, the biggest hint that Inquisition could correct this come Dragon Age 4 is arguably in The Descent DLC.
Dragon Age: Inquisition - The Descent and Dragon Age 4
The Descent DLC, in short, puts everything known about the dwarves and Titans into question. Investing earthquakes on the Storm Coast, the Inquisitor meets Shaper Valta and a Legion of the Dead Lieutenant named Renn. Going far beneath the Deep Roads and dealing with the Sha-Brytol, Valta eventually discovers clues about the Sha-Brytol, the Titans, the Wellspring, and more, ultimately culminating that with the discovery that the players are in the Titan itself. This ends the Dragon Age: Inquisition DLC will tons of questions, but perhaps the Titan mystery is second to the fact that Valta appears to use magic at one point.
It seems that the Titans are being set up to play a bigger role, perhaps by somehow being tied into the current mythos of the Elven Gods and the Maker, but Valta has to play a bigger role now too. Criminal, it would seem, if Valta was a Dwarf, capable of some type of magic, but not a companion in the next game. The entry point to explore her backstory, the Titan's background, and tie it into the overarching story would be best with a permanent Valta companion in Dragon Age 4.
Then, presumably building from the ground laid by Scout Harding and the latest technical innovations, Valta could also be the first Dwarf in the franchise to be romanceable. Of course, this is mere speculation, but to make sure the Anthem with Dragons criticism does not land, Dragon Age 4 needs to go all out. This is one clear way of doing just that.
Dragon Age 4 is in development.