https://theathletic.com/4684339/2023/07/11/usl-promotion-relegation-system/
If enacted, the USL would be the first open professional league system in modern U.S. soccer history.
Not directly MLS related but I think it's worth noting
Pro: Every match is meaningful. That mid April slump where your club drops 6 points could be the difference between a poor year and one where they get relegated. End of season matches between the worst clubs will get spicy. It allows smaller clubs that punch above their weight to earn better competition. Who wouldn't want Forward Madison in the top USL club. Who wouldn't laugh their ass off if Louisville got relegated.
Cons: How will this affect the CBA for relegated clubs. Does this create an arms race where the most monied clubs succeed. I'm not sure how USSF Professional League Standards will have to be amended to allow a small club in small city exist at the top of the pyramid.
Overall the cons are limited. It definitely raises the value of current League 1 clubs because they are 30 something matches away from being in the Championship. Potentially this will create more news interests and hype. It creates a meaningful difference from MLS other than not being MLS.