Niantic announced that a new Capture Bonus to increase the odds of catching rare Pokémon in Pokémon GO will be coming to the game soon.

Earn a New Capture Bonus to Increase the Odds of Catching Rare Pokémon

Trainers, We want to give you a sneak peek of a feature coming soon to Pokémon GO. We are adding a new feature which grants a catch bonus when you earn medals based on catching certain types of Pokémon (Kindler, Psychic, Gardener, etc.). These new bonuses will give you a better chance of capturing Pokémon with a related type. For example, as you reach a higher tier for the Kindler Medal, your bonus to catch Fire-type Pokémon such as Charmander, Vulpix and Ponyta increases.

Trainers can work their way to a new tier by catching many Pokémon of the same type. If a Pokémon has multiple types, your bonus will be the average of your bonuses for each type. For example, Pidgey is both Normal and Flying type. Your bonus in this case would be the average of your Normal-type and Flying-type bonuses.

Look forward to this new feature coming soon!

Source: http://pokemongo.nianticlabs.com/en/post/elemental/