This is one thing I really wish we had. There are a lot of potions, poisons, scrolls, and food that I get that I have little use for and it would be nice to be able to convert them to gems to open up the bag/bank space without having to destroy an orange item. It can be a minor amount of gems, even 1 gem for a stack of poison or an exp scroll would be enough that I would be happy to convert them.
Even the orange character bound items we get during leveling could potentially qualify, it is the opposite of P2W as we are taking in game items that affect character performance and converting them into gems for cosmetics. There are so many of those items in my inventory just taking up bag space and they are character bound so I cannot even bank them..
This would give ESO+ members access to some free gems without having to spend their ESO+ crowns on crates.
If anything once people get some gems stored up and get close to a gem purchase they want it would probably actually encourage some people to get a crate or 4 to get the remaining gems they need for an item once they get close to the amount they need.