Hey @Zaire22, this was suggested in the past already and was answered from a dev as well.
About your idea on getting the chance to release a pokemon when your box is full, I dont see the purpose to be honest as there is already a warning ahead of time via an icon on the top-left which tells you to clear out some space in your box.
However maybe we are getting something new regarding that with the box update in the future.
https://pokemonrevolution.net/forum/topic/156698-a-release-tool/?do=findComment&comment=867827