I know CP is perhaps the most visible metric to determine how strong on weak a pokemon is, but trying to make a decision solely based on any of these two metrics may not be a good point of reference. For instance I wouldn't want to transfer my 148 CP Magicarp, but I definitely don't want to keep any Meowth below 400 no matter how good of an IV they might have. This is why I please ask you to include an option to discard any pokemon below a certain stardust level (which is the closest thing to estimate the pokemon level) This way I can safely transfer low level pokemons no matter what CP power they might have.
This is already a thing. In your settings there's an option to take both CP and IV into account before transferring a Pokemon.