Given that the outcome of a natural force moving a ball can be disadvantageous or advantageous - quite possibly over a period in equal measure - how can it be said to be punitive? In what way isn't it neutral and equitable?
Don't get me wrong i don't think the rule is inequitable. I agree it will balance out given time, it was more along the lines of it being unnecessarily punitive.
I suppose one to look at it could be that when it favours a player it becomes punitive to the field/competitors. A player may select a location to take relief where there is a possibility the ball might roll towards the hole.
I understand the concerns regarding when does a ball become in play if this rule was to change but i don't think it would inherently be a difficult rule to work out. You could argue that it would likely go against the simplification brought in with the 2019 changes but considering how rare this would occur a simple note along side the rule wouldn't be the worst thing in the world.
Something along the lines of "if a ball dropped in a relief area moves out of the relief area before a stroke is made the ball is to be be re-dropped in the original relief area with no additional penalty"
I'm certainly no expert but i think it could be worded so that is doesn't specify whether the ball is play or not. So that regardless if the ball comes to rest or not, if it leaves the penalty area before a stroke, it gets re-dropped.