I don’t think the change to the 20 th is especially significant in itself. Nowadays cong reports in most countries are filled in online , so you don’t need to allow for postal delays , “lost in the post” reports that need to be chased up by Bethel or negligent secretaries who always missed the deadline. Informally the service desk (at least in the UK) didn’t start collating the figures till the middle of the month anyway, as there were always a few stragglers.
If (and it is a big if) they are stopping reports altogether , then that is a big change. As many have suggested , the discipline of doing so does force many to go out , as per the number who go out on the last day of the month. The WTS would be loath to give up this procedure , even though it has absolutely no scriptural basis (if anything , it is against the scriptures). I’m convinced that the only trigger for this would be a change in the legal basis , ring fencing the WTS from any legal obligation towards the majority of Jws.
To paint an analogy , if a spectator punches you at a football match , you have no case for suing the club or stadium owner (unless some negligence can be proven - very difficult to do). But if a volunteer ( eg a club steward or burger flipper ) does likewise , you have a valid , easily provable claim.
Define a volunteer. Even though unpaid , he directly receives instructions from the club. He reports his activity to the club on a regular basis & accrues benefits from it.
At a stroke , the WTS removes any obligation - legally , socially - from the majority of it’s members. No doubt office bearers (such as elders & Bethelites) would still (legally) have volunteer status. Pioneers are a bit of a grey area but they are (supposedly) appointed directly from the branch and the WTS turned the legal basis in the past against pioneers and successfully DF them.
OK now. 2010 - little Johnny is being abused by a R&F JW Bro Paedo. His parents go to the courts to seek redress. The WTS lawyers successfully argue that the individual was simply someone who attended the meetings , perhaps on a irregular basis. He wasn’t a member / shareholder / stakeholder / employee / volunteer of the WTS. Though he did go on a Christian ministry , this was as a member of the local congregation & there wasn’t any connection whatsoever with this activity and the incorporated body of the WTS. “We have no record of him , we aren’t responsible for him.”
This begs the question - how do the WTS now “police” individual Jws & ensure that they are going out? The onus is much more on the Group Overseer (GO) (I forget the new title) to ensure that he is very familiar with the activity of his flock. In the past , brothers could go to other arrangements or out with family & hardly ever work with their group. The GO needs to determine who is going out , when , how much - especially if he doesn’t see them going out with the group. A simple summary of activity at the end of the month - total number of who was out in his group - would be all that was needed.