I am a little confused. This isn't a change in the law, it's just highlighting the issue of consent, no? It's not saying people are guilty until proven innocent.
It's kind of like in medicine, you don't need express verbal consent to take blood from someone - you just say what you're planning on doing and if they hold their arm out, that is consent. Similarly with this, if they are actively participating then that is consent, you don't need a signature. This new thing today doesn't somehow change the nature of consent to suddenly needing to be a verbal or written contract.
It just makes sure that people will ask an important question in interviews surrounding these crimes. It doesn't somehow prejudice the answer or raise the standard of consent (it's always been wrong for instance to have sex with a virtually comatose drunk!). To be honest it's a question which they should have been asking anyway - probably many were.