Meding Balancing Idea

I've been thinking about the new Villager balancing a lot and I do certainly think that moving Mending to swamp villagers is a good idea, but it still makes Mending too accessible.
I had my own idea for Mending. A villager that only spawns in Ancient Cities - curing a zombie Villager won't work. However, it doesn't just give you Mending on it's first level, you need to reach the villager's max level which you partially get through trading - like every other villager - but this special villager will also give you Quests you need to complete to level him up. Also the trade will be blocked for an in-game week after you got one book. So you have to work for Mending, it's a bit of a grind, you need to leave the city for the quests and then you only get one book every few days (that part can be worked on to be more challenging or something)

Like I said, the balancing they work on is a great step in the right direction but as soon as you have a Mending Villager in a swamp it's the same as before. Minecraft needs better progression and I think that this idea here is a good step towards that progression. Mending is a powerful enchantment that shouldn't be that easy to obtain. This system I'm suggesting would have players thinking about which tool to use their one book one. 
Thank you for reading.