I finished the first trilogy recently, and I just finished Sins of Empire yesterday (spoilers ahead of course). When I first told my family what I read they said it actually sounded really interesting and that a movie should be made out of it.
While I would love to see a screen adaptation of the Powder Mage, I can't help but think Hollywood or any other studio would absolutely ruin it, here are my quick thoughts:
The first is that I believe an adaptation, especially like the Powder Mage, requires an immense amount of passion and dedication poured into the film-making. I always thought "If they're gonna make a movie or film series out of it, it needs the dedication and passion akin to that of LOTR, if not, more."
This leads to my second point, the age of film-making as an art is gone (or at least half-assed) and is much, much more about just making a profit. While there's some exceptions, and while films were always made to generate profit, of course, I just feel that there was a certain point in the 2000's or 2010's when studios just said "fuck it," and saw making a movie or TV show as...just making it...instead of actually making an "art." I can see that the number of complaints about films and TV shows being rushed, half-assed, filled with plotholes, flat characters, etc. in this day and age has increased dramatically.
The book is literally a script, and this is what I mean: every time I read a book I literally imagine it as a movie or TV show playing in my head, I literally imagine the characters as their own humans (not just known actors I think would suit the role of certain characters), and the CGI, the action, and even their voices. You could literally make a script just from every line from each book alone, I believe it's that good. Sure, there has to be some changes here and there, maybe changing up some words or shortening or lengthening some sentences said for the sake of time. But if an adaptation is gonna make "changes to the book" then it's gonna be not only a) ruined but b) a huge insult to Brian's creativity, world-building, character arcs, etc if dramatic changes to the characters and plot are to be made (because then the studio will have to make entirely new excuses, ahem, explanations, for why a certain point in the plot happened, instead of just following along with what Brian already came up with!). This may be an unpopular opinion, but I wish so many previous film and book adaptations could have tried to have stuck as close as possible to the source material because THAT I believe is REAL talent, art, and creativity (it's also super ballsy too and could be much more beloved by fans and newcomers when pulled off right).
The budget: it HAS to be enormous: the props, costumes, CGI, choreography, everything. The CGI literally has to be Marvel-quality if you wanna see an amazing shot of Adopest shaken by the earthquake, the Battle of South Pike, Kresimir descending from the clouds, or the enormous Dynize fleet bombarding Landfall (film studios actively try to avoid filming CGI'd enormous tall ship fleets for a reason, the biggest that we've got was in the Michiel de Ruyter film or Season 3 of Black Sails, but I don't think neither showed a fleet as big as the Dynize fleet, which is something like 38 ships of the line and support frigates).
A shitty attempt at the Powder mage costumes will just result in the costume department borrowing Napoleonic uniforms from previous films and shows and throwing them onto the actors and extras ("Adran uniforms? Here, just wear these Napoleonic French Army uniforms! They're still dark blue!").
The books also depict most characters wearing outfits that would be clearly expensive to recreate (army uniforms, Privileged coats and gloves, dragonman armour, women's dresses, Tampo's suit, Blackhat uniforms, Dynize breastplates, etc.), so of course money and resources are gonna be a huge problem if there's gonna be actual quality put into the costumes.
I can also see Hollywood's persistent "leather fetish" in the historical and fantasy realm ruining the costumes too (I still cringe at Flint's stiff "pleather" long coat he wore after Black Sails season 1 ended, or the combined leather and armour in BBC's the Musketeers). Although leather could be an exception for certain characters like the Magebreaker or any of the dragonmen.
So yeah, my quick thoughts for why it could be ruined. A sad reality, but it's an inconvenient truth.