In a nutshell, the 17th is looking for ALL circuits to be RCD/RCBO protected, so where, in a bathroom you may have had underfloor heating installed on a ring(RCD protected of course!!), plus lighting, and will, of course, have linked your supplementary bonding to both local circuits cpc (lighting and underfloor heating etc etc) you will now have (preferably) your lighting on a separate RCBO so that your lighting will stay on if there is a fault with the ring cicuit. Expect to see split/split load boards or just use an rcbo on each circuit. The good news is that if the new requirements are properly met, there will be no need for miles of 4mm bonding, so you can flog all your rolls of 4mm g/y to anyine who hasn't boned-up on the 17th!!