I think that some Hiltons have been doing this already. I had a stay at the Munich airport Hilton a few months ago. About 2 hours after checkin housekeeping entered just after I had got out of the shower. This was despite the do not disturb indicator being on and the door locked (there is no deadbolt, just an electronic lock which housekeeping can over-ride). Obviously I was hopping mad and complained. The manager, while sympathetic, said that they always check the room every 24 hours. To be fair to him, he agreed that this should not be 2 hours after checkin.
What worries me is that if this is official policy, hotels will use it to justify mistakes which are an invasion of privacy.