I don't see this change happening, it'll stay as is.
Someone noted that in the UK they don't do this, but that's incorrect. England made the change to year groups for FA groupings around the same time or just before the US. That said, there is a huge schools based soccer system in the UK and that remains grade based.
From my perspective my kids are Sep & Nov, so both were impacted by this.
On my son's team (Nov) they were about 50-50, older (Aug-Dec) vs younger (Jan-Jun) and the backbone of the team were the olders. They were also a top team in the state. Roll on from the change and all bar 2 of the "olders" have left soccer and all the "youngers" play DA or ECNL. They were not better players than their old teams mates, but they were dominant vs the "olders" on the year below.
On my daughter's team (Sep), they were about 20-80, older (Aug-Dec) vs younger (Jan-Jun) which was a strange mix. They were an avg team in the state. The "youngers" are now probably the top team in the state and only my kid is left on the "olders" team. That "older" team is made up of 90-10 with 90% of the players being Jan-Jul.
One thing I notice (I look as my kids are on the younger side now) when looking at elite rosters (DA) - on the girls side in particular, the older kids dominate. Its a biological and maturity (a grade ahead) advantage. On the bright side, if my daughter can continue to hang, she will have a huge advantage over her peer group if she wants to play college, as the number of kids from her grade year playing elite soccer in the Aug-Dec months will be far fewer than the number in the Jan-Jul months - and she will be playing a year "up" relative to her graduating year.
That said, I've never agreed with the change given it's not designed to service or support the kids in soccer. It doesn't surprise me that numbers have dropped.