The ruling may have some interesting impacts:
1. At least from a mandatory having to play a certain age level, they principally turned 18u into a Seniors only age group. Some organizations may have 16u eligible kids play 18u for various reasons including roster balancing, but for the most part it may make it harder to fill some 18 rosters if the talent base you draw from is strictly Seniors.
2. One of the long running complaints about the Jan 1 rule was it divided teams at 14u between 9th graders and junior high kids. Which created scheduling challenges in the spring. This change does not solve this issue and actually increases the number of 9th graders likely to be playing 14u.
3. It does match the age groups by school class better because it follows the school birthdate calendar, but because of the two year increments in softball, you will still have 2 and 3 graduating classes well represented at 16u competing against each other. For example you will see 2027s, 2028s and some 2029s playing 16u next year.
4. If you buy the argument that 16u is where the coaches are, this rule likely will magnify it even more by adding the Sep 1 to Dec 31 Junior class to the 16u mix each year. As I said, it shrinks the talent pool at 18u dramatically. By the time summer rolls around, with the 9/1 to 12/31 portion of the Junior class now playing 16u, you will find the national level teams that take advantage of holding kids back at 16 will have all or a large portion of their rosters already recruited by June.
5. Have to keep in mind, rostering around these rules will be at the discretion of each team. Some kids will play "up" for any number of reasons, but you would think that very large programs may build their rosters around keeping players "down" from a national competition standpoint.
6. Most people would agree your sophomore year and summer before your Junior year are the most critical 12 months from an evaluation standpoint. That group will now find itself competing against more older kids than before while being first year 16u. For college coaches that may be a plus, but for the athletes who elect to play 14u as 9th graders (which will be most) they better be ready to compete against a more experienced group of players at 16u than in years past. It may just be a coincidence, and there are some exceptions, but my first Juniors recruited each year are the 9/1 to 12/31 kids who had the benefit of being in year 2 of 16u during their sophomore year in HS.
7. I do believe each age level is more challenging than the age level below it. You have to do things better to have success every time you move up a level. It has been my opinion that the 9/1 to 12/31 babies historically have benefited from being forced up the chain a year earlier than their HS classmates.
8. If your organization is not large, and you don't have the luxury of "loading up" with old kids at 16u, I think you look at your rising Junior class members that are most likely to be recruited between 9/1 of their Junior year and the start of the six week recruiting window in fall and plan for them to play 18u to help play fill your 18u roster. However in smaller programs you may not have that luxury as roster spots may need to be position driven also.
Until we experience the new age parameters you can't predict all the outcomes. I am sure it will present challenges. In the end, good knows good and therefore "good" likely has nothing to worry about. You probably shouldn't overthink things - though I just wrote an essay doing just that. In the end, revenue sharing and NIL will likely have a greater impact on the future of player recruiting than the age rule change.
