The above document describes the existing paper-based process and I believe the only thing it proves is how cumbersome it is for foreign nationals working legally in the UK. I don't understand what you mean by "mandatory for everyone", because the rules for UK nationals do not change:
> If you’re a British or Irish citizen, you can prove your right to work in the UK with either of the following: a British passport, an Irish passport or passport card. Your passport or passport card can be current or expired.