I’m thinking it might be easier to make a case for requesting new armor that is thematically similar to what you want but with an adjustment to conform it to light, medium, or heavy as the target type. I mean, not to ask to be able to to use actual heavy armor items on a light armor user but you could ask for light armor items that have a similar aesthetic or style. (I would personally be more in favor of a proficiency system that let any character use any item or gain any ability but that means throwing the classes overboard.)
It seems that there’s no prejudice against the idea of cosmetic gear because that’s what transmutation does now. There’s also no pure logic dictating gear must match class because there are heavy armors that look like medium or light armor now. What appears to be the issue is the ability to recognize a class because of its armor. This is not a strong argument. It would literally imply comprehensive knowledge of the available armor sets for every class. It also makes no distinction between classes with distinct abilities such as Thief vs. Engineer. These two classes can look virtually identical but they do not play the same way. Warriors and Guardians are not clones of each other but can look very much alike. Mesmers and Elementalists can look alike but I doubt I’d base a comparison of them on their armor. Also, the look of armor has only so much to do with its stats. My gear, with heavy armor, might still be more statistically similar to the gear of a Mesmer depending on how we built our sets. Looking at our gear wouldn’t tell you that. Looking at my gear would not presently tell you whether I prefer +toughness, +power, +healing, +magic find, etc. It would only tell you that I look like a heavy armor user. Good luck figuring out what that means without playing with me or watching me use my skills.
Then, regarding aesthetic consistency, the issue is really whether it will end up being more desirable to allow players to determine their own aesthetics or requiring them to fit a certain standard. I believe most of us would prefer the standard to that freedom if the result was going to be that a large percentage of players made their characters look ridiculous. This seems like a reasonable concern. However, I have one problem with it. The very best way to make sure that no player looks ridiculous is to control the elements from which they can construct their look. So it suddenly seems a little weird to say that a Mesmer would look bad wearing something that would not make a Guardian look bad. If the armor is quality controlled before it ends up in the hands of players then I think the odds are actually against the players being able to make a lot of fashion mistakes.
Lastly, there has long been a holy grail of sorts with character creation in MMOs. Character creation is an absolutely HUGE interest of MMO gamers. It is a really frequently voiced desire to be able to make a character that is personally recognizable. When you encounter my character in the game I would like you to note that character’s name, pay attention to the design of its features, and notice how I’ve customized the appearance of my gear. The further and further you get from features that support this ability the more dissatisfied some gamers become. I’m lucky. The art department for this game has been very good with providing me with gear I like and character creation options that fit my idea of my character’s design. I personally believe the OP’s request reflects a positive attitude toward character creation potential in the game. If you continue to expand the options for this process and provide solutions when players feel unnecessarily restricted it will surely create successful identification between players and characters. That adds so much to every player’s motivation to play their character.
Therefore I support the examination of the process for providing cosmetic armor and the extension of that process toward greater realization of each player’s vision for their character’s appearance.
