What would you accept for a "better" DA4?

Well, from my perspective, it has in fact, almost all already been done before. At the risk of pissing some people in here off: The story structure of traditional JRPGs is where I would turn for inspiration (off the top of my head, Final Fantasy X and prior entries in the series are good examples of this). In a traditional JRPG, the main story/critical path tends to be much longer, usually the bulk of the game is main story content. Character arcs and side-plots are resolved in the course of completing the main story, much like they would be in a novel or film. The members of a JRPG party also tend to be more personally tied to the events of the main story (ie, all their personal goals are somehow related to the main narrative), unlike in a BioWare game, so taking time out to resolve their personal arcs makes more sense/is easier to justify. And while JRPGs do still have side content, in the past it was rarely labelled as a "side quest", and it usually takes the form of secret dungeons, challenging 'boss' fights, and minigames that provide variation in the gameplay (it's common, for instance, for JRPGs to have a 'Casino', where the player can play games of chance and earn tokens to trade for prizes, which normally are powerful and unique pieces of gear that can't be found elsewhere)

Similarly, many JRPG plots also require the player to embark on an epic journey that spans the entire world of the game, rather than just across a single country, and plots almost always involve 'surprise' twists/reveals regarding the nature of their world, so world-building occurs naturally, and you can pretty much guarantee that you're going to learn a lot of lore. There are also plenty of moments of low tension, although these usually take the form of cutscenes or dialogue between party members, where they have their heart-to-heart discussions, reveal their backstories, share secrets, form relationships, etc, etc. This is also where the romance typically happens, although it's usually between two fixed characters. JRPGS aren't so much about choice, and when there are choices, they rarely have significant impact on the main plot, although there are exceptions.

So basically, I would just add BioWare style choice/roleplaying and romance elements to the narrative style of a JRPG. The JRPG genre already has games like Persona 5 that allow a wide scope for choice (albeit in a very different way from BioWare), so I don't think it would be impossible to implement.