On Gaining Mage and Templar Allies
One gripe I have with Inquisition is that we can't "officially" recruit both the mages and Templars, especially when bands of both join you anyway (depending on your choices). While I realize there are many years' worth of extremely bad blood between them, the Breach and outbreak of the civil war between them are—especially combined—would've been a very good reason and excuse to at least tie a truce and reform option into the mix.
(TL/DR: This will break down ideas for small adjustments that could build an alliance on both sides in-game without any significant changes to the game's structure or overhaul of the story. For the sake of keeping it simple/universal, I'm operating with the default world state DA:I gives you. This particular post exclusively views this from the mage choice perspective).
There doesn't need to be a question of story scope or game volume. You could even still choose your initial alliance the same way and bring the second party in through war table options later on. Even if my Inquisitor chose the mages, we still could've had an "in" or start with the Templars through Ser Barris's obvious discomfort with the direction the Lord Seeker (which, the fact that wasn't even Lucius alone is another point I could dive into) and Chantry were taking in Val Royeaux.
Barris is perfectly set up from the moment we meet him as a potential leader with a more perceptive eye and level head than those around him. He publicly questions his superior and asks the all-important question of, "What-if?" He's already seeing that something's not right or isn't adding up, and if he's bold enough to call that into question, would it be so far-fetched for him to send a letter to Cullen to start talks with the Inquisition?
Minimal changes could be added to existing war table quests. My mage Inquisitor might be unusual in that she both recruited the mages freely and actively utilizes Templars under Cullen's command. I share this because there are several options to do so through which you could easily slip Ser Barris's name in as the correspondence and be growing that alliance/planting those reform seeds in the background without any real overhaul of the story.
Just like we have Rylen as our armed forces contact in the Western Approach, we could have Ser Barris serving a similar role when it comes to Templar activity. Maybe he's even able to get valuable intel to Leliana that helps Cassandra's quest.
No cutscene would be necessary, but a shorter version of the Champions of the Just scene where the Inquisition takes on the Templars as allies could be used where the Inquisitor meets Barris personally and the band of Templars he leads that's broken off from the Red Templars.
We already know the Red Templars are trouble if we've sided with the mages. We don't need to add anything for this to make sense if we've already had those little seeds through Val Royeaux and war table quests planted.
We've all spent enough hours in this game to hear how many are sick of the fighting, and we know too that people are starting to have ideas on how to start improving relations between these two groups.
Let's iron out the wrinkles and give Cullen's idea a test run before any new Divine is even chosen. It's not perfect and needs more development, but there's no more perfect group to try it on than mages and Templars who've already agreed to ally through the Inquisition.
(Note: I've noticed some give Cullen flack on his plan of allowing mages to work outside the Circles with Templar support, but in my opinion, the fact that he is trying to think of solutions to make things better for everyone matters a great deal and shows tremendous growth. It's not a perfect plan, but it's a good start with what control or sway they have in the matter. We have to remember that it's not just mages and Templars who are impacted by all of this, and the Average Joes of Thedas have more than enough reason to fear forces they're practically powerless against).
Too many men in armor with the same ideas can be dangerous.
So can too many in robes with staves. Mages are no less susceptible to blind arrogance and corruption. They are, after all, people too.
Radicalism, self-righteousness, and a drive for power are dangerous no matter who's wielding it.
Lean on seasoned mages who are sick of the fighting like Ellendra (she doesn't want any part of the war, so give her an option to partake in the peace/healing efforts) and a trusted Templar like Barris or Lysette to work together to lead small initiatives that work along the lines of normalcy. Hire the cute elf kid from Redcliffe to help farmers start regrowing their crops/building a prosperous harvest at the Crossroads or Redcliffe Farms.
Everyone needs food and supplies to survive. Get them working together on the fundamentally human (for lack of a better term) level to equally contribute to a shared need and practice. Get them working with the Average Joes (non-mages, non-Templars) in a way like this that benefits them and shows them ways in which magic can be used for growth and healing instead of destruction. Show them the Templars who want to serve the Maker and protect the people of Thedas.
Show the Joes both groups working in equal unison to take out Red Templars or demons that threaten them. All of this can still be under the unified banner of the Inquisition, and let word of those experiences travel naturally (and elevate word of the allied heroics through Josephine and Leliana).
Let people on all sides see these groups working together as equal partners and start figuring out the best ways to govern themselves while they already have a unified front to work from. There will still be issues and still be "scuffles" to use Fiona's term, but having a strong group of allies can help better, more developed, and stable tactics emerge.
Let this trickle into Divine Victoria's (mine's been Leliana both playthroughs, but this would help Cassandra a lot, too) reformation plan and strengthen her foundation for it. Vivienne would be a bit give or take. Perhaps even appoint a trusted Revered Mother as advisor to the Templars (Giselle comes to mind, for her insightful criticisms of the Chantry, dedication to the Chant of Light,and willingness to correct herself).
You take out the lofty idealism of a shared goal of what we'll for convenience's sake call "good" mages and "good" Templars by putting it into practice using small steps. It becomes less "radical" then when Divine Victoria drives change when more people have been in direct contact with the benefits of that change.
It's very true that such an alliance may never last: too many egos and too many self-serving hands in the Game always do seek to ruin the good others have built.
So let the Inquisition become a bold symbol of the good that can be done when people set aside their pride beyond just sealing the Breach or saving Thedas from one ancient moron or another. Let it be a place of healing and, maybe for some, redemption.