The painter villager is a new type of villager. The painter spawns in his own house which has a few chests and multiple paintings.
The painter buys dyes of all colors, flowers, and occasionally wool. He sells normal paintings at 1 emerald for 4-5 normal paintings. However, the painter also sells certain unique paintings (that you cannot otherwise obtain) for 1-8 emeralds per painting, with the price depending on the rarity of the painting. Most of the large (3x3, 4x3, etc.) unique paintings are rare and expensive. There would also be some new paintings that are only found in dungeon chests, which could be sold to the painter villager for 9-30 emeralds, or kept and used for decoration.
You can also buy portraits. There are several portraits you can buy:
Player Portrait. (3-7 emeralds)
This is a 1x2 painting of the front of your player skin with a terracotta background. Any armor you are wearing is included.
Heroic Portrait. (6-8 emeralds)
This is a 4x3 painting depicting your player running with a diamond sword and diamond armor while fighting a raid. If you buy this while riding a horse, the painting will show you riding on a horse with diamond armor in the raid. Requirement: Have "Hero of the Village" effect while buying the painting.
Zombie Siege Portrait. (9-12 emeralds)
This is a 4x3 painting that is like the Heroic Portrait except it shows you fighting zombies instead of pillagers. Requirement: Have the "Monster Hunter" advancement.
Dragon Slayer Portrait. (11-15 emeralds)
This is a 4x3 painting that shows your player in diamond armor next to an Ender Dragon on top of endstone. Requirement: Have defeated the Ender Dragon at least once.
Wither Slayer Portrait. (11-15 emeralds)
This is a 4x3 painting that shows your player in diamond armor with a bow fighting the Wither. Requirement: Have defeated the Wither at least once.
The game would take your skin texture and use it for these paintings. After it does this, it would save the painting's pixels so that if you change your skin the painting stays the same. This would allow adventure map creators to have halls with many different portraits in them.
These paintings would also be customizable with texture packs. Each painting texture is completely white in the places that the player heads go, and completely purple where the rest of the player body goes. In the paintings other than the Player Portrait, only the front of the player head texture is used.
With these additions, there would be more paintings to customize your house with, more reasons to explore since you can find special paintings, and new ways to depict historic moments within your world.