Here’s my problem with gender locking as it is currently utilized and talked about (and I think this ultimately encompasses how nonbinary ROs are conceptualized as well).
Keeping things flippable and open is very often the only way we can get gender role and presentation diversity injected into these stories. And speaking as a cis bisexual woman with a strong interest in androgynous/gnc (gender nonconforming) people, this is sometimes essential for my enjoyment of a game, and I am certainly not alone in my preferences. (I mention this to be transparent, and not to suggest that my argument for diversity is so my libido is happy. I am not part of the group I am advocating for, just an interested party in their visibility.)
Keep in mind I am speaking in generalization about a trend I’ve seen through many, many games and WIPs. There will obviously be exceptions to this (ones I am always very pleased to find), but I am focusing more on an overall repeating pattern.
As an example, while there is a valiant push towards diversity in this community, it is still the case that 8 times out of 10, the soldier/knight/fighter/stoic/aggressive character will be male and the mage/rogue/charmer/diplomat character will be female. Because that is the default, being able to flip the gender of these types of characters is often the only time you get any variation (even in only profession/skills! This example doesn’t even touch appearance.)
It is also often true that the male character will fall quite heavily on the masculine side and the female character will, in turn, fall quite heavily on the feminine side (in appearance but also mannerisms). Locked gender ROs often follow this pattern, even when the ROs’ sexual orientation stays open. But that same scenario with gender flippable characters? Now you can have a strong female soldier and a soft, clever male mage (something that is rarely chosen by the creators on their own). I tend to choose these options even when I have no interest in romancing either of these characters purely for diversity that is otherwise not provided by the games itself.
Some great examples of what gender flipping can produce would be Dandy from Evertree and Julia Ortega from Fallen Hero. Dandy feels quite femme to me, as if the initial template was Daisy, a very feminine woman, and then her gender variant was created out of it. Would Dandy have been as he was if it was only him from the beginning? I don’t know. I hope so, but it is also the case that I only see this type of gender presentation difference in flipped characters. Julia’s physicality, strength, and even the way she speaks and holds herself feel quite unique to female characters, and I know Ortega was originally only male. Gender flipping can give combinations of traits that creators wouldn’t initially think of (and even help in getting past unconscious bias). And maybe that alone is the main value for gender flipping as a continued creative tool. Creating two separate characters with the gender swap, as OP mentioned, could easily fall into the initial problems with locked gender characters.
Overall, these initial choices by creators and writers are still very predictably followed by the cultural standard. (I could easily go into a tangent here about how m/f romance is written and how they almost always quickly descend into standard gender role tropes no matter the characters’ personalities, but that’s another rant altogether.)
Which brings me to non binary characters. Right now, gender nonconformity in locked gender characters falls almost entirely on the shoulders of non binary ROs, which is itself a problem as non binary is not synonymous with androgyny but you wouldn’t be able to tell that from looking at CoG/HG games as a whole. As it stands, the default template is Female RO= feminine, Nonbinary RO= androgynous, Male RO= masculine. A little reductive, no?
Now, I realize game creators are not making these decisions in a vacuum and are a lot of the time reacting to what they feel their readers want. (I certainly watched this happen with Wayhaven as people gave advice on how to gender-ly touch someone’s shoulder. Did you know if you’re a man, you can’t touch your elbow when you’re nervous? It seems so, going by some of that feedback.)
I also know a lot of game development is feedback going in both directions. You want to make likable characters that the majority of readers will enjoy, and a lot of people are completely fine with the default template. I don’t have an easy solution to present with all of this. Do I wish creators made less gender role-adherent characters in general, whether ROs or not? Absolutely. I’d love to see more women in character roles and narratives that are traditionally given to men and vice versa. I’d love to see people questioning the gender they make a character before solidifying it. In the long run, that tends to make more interesting, unique, and memorable characters for the audience.
I’d love to see more diversity in non binary characters so we don’t run into issues like what @HannahPS mentioned about reactions to a nonbinary character being too feminine and masculine at the same time (which speaks to deep confusion about what a non binary person looks and acts like, which can be remedied with more diverse examples). I’d like to see us move away from non binary tropes like devious/wise tricksters always wearing neutral robes.
I think using gender flipping for diversity is not where things ultimately should stop, because I think that diversity should be within the writing at the beginning. All I know is until that happens, I will be protective of this option as a bandaid that lets me keep easily enjoying these stories (and putting my time into helping make them better, however I am useful).