I hate to even open this can of worms but it fits with the line of reasoning from earlier posts. Little Chicago: Harry projected himself outside his body using that device.
If Little Chicago still exists could it be used to breech the 4th dimension? Maybe Harry can leave his body without it now that he has more experience being out of body. LC is just a focus, though extremely complicated, magic can be performed without a focus.
Sits back to watch the speculation.