I wish they would add more...would keep the game more interesting during long stretches without much new content. There are so many Pokémon that are completely useless to the current meta.
Let's compare two Pokémon that are basically useless in the current meta and how we look at them. Look at pikachu and slugma. Both have an evolution at 50 candies and both are useless as gym attackers/defenders/raiders. They are also both pretty difficult to catch compared to a lot of non evolved Pokémon. If I see a slugma, I walk on by...it's not worth the time, resources and possible frustration of catching it. If I see a pikachu, I always click on it just due to the fact I want the shiny variant (still don't have one).
Now imagine if all the Pokémon were that way. You would click on almost everything just because you want the shiny.