Let me first start by saying that I love how much we are able to customise our characters in ESO. Its wonderful how many different outfits, hairstyles, adornments, body markings, etc etc there are to decorate and dress up our characters with! However some of these options have certain limits. The big one being unable to equip a hairstyle, adornment, etc if you are a male or female character. The other being unable to equip certain body/face markings and facial hair depending on race (this I am more forgiving with, but I still think there should be a few exceptions).
A lot of the customisations in collections that are locked from equipping, are pretty old in terms of game age, and I think have been forgotten about and been overlooked. They are parts of various crown style parlour packs. More modern style packs, and appearance collections from crown crates or monthly rewards are never gender or even race locked. If I may provide an example:

This is my Male Altmer. He is wearing Barbaric Windblown hair, Eye-Briar gemmed tattoo, Dark Emphasis Eyelashes, Cherry Blossom Anadem, Dangling Triple chain Earrings (not that you can see them), Bardic Tavern Singer's Dress, and Thorns of Ecstasy Body Markings. As you can see he looks pretty female (this is my drag outfit...), so if I can dress him up like this, why am I not allowed "Crimson Begonia" or "Imperial Moonstones"? My hair cannot be in braids or pigtails? I cant put on pearl earrings?
I'm not saying I want these things unlocked just so people can dress up their characters as the opposite gender. Some of these hairs, adornments, etc work perfectly fine with a traditionally male look. My Male Mage might want to wear ear rune earrings and a scholar's half circlet! Considering that all modern collection items are allowed to be worn by either gender, I don't see why the old ones should still be kept locked away. I can't actually speak for stuff thats locked for female characters, as I have only ever played as my male Altmer (playing since 2016 and still on 1 character haha), but I'm sure there are male only adornments, hairs, etc that female characters would like! Might I also remind you that we are in Pride Month at the moment, so this would be a nice gesture on your part...
In terms of race locked customisation options, things are a little more complicated. But certain things, like Khajiit feline body markings, I feel could easily be translated as normal tattoos on Men and Mer. Similar to how one may wear a leopard print dress, one might also have a leopard print tattoo, or tiger stipe tattoos. Bring out your love of cats in your Man/Mer! As for Argonian scales, I am less sure on how that would work... But I have confidence it could be translated into a tattoo in some way or another. In facial hair, there are various horn types that can only be worn by Wood Elves or Argonians. It would be nice to be able to wear these as any race (though not a deal breaker) as it could be explained lore wise as them being prosthetics, Magical growths, or Appearance illusion magic! Considering we have skins that give us scales or turn us into Ice, and Polymorphs that turn is into Daedra or goblins, I don't think asking for this is really that much of a stretch to ask for.
I think its bad value for money when you buy these packs especially on the crown store, and you can only access half of what you paid for!
(I also think we should be able to put Major (and maybe Minor) adornments on our companions. I understand not wanting to cover their head, and so certain adornments would have to be exempt like the grave elegance mask, wire cage half mask, and belly dancer veil to name a few. But Earrings and circlets should really be allowed! I may make a more detailed forum post on this however.)
Thank you for listening to my whiny rant
Let’s have some fun this beat is sick, I wanna take a ride on your disco stick.