Not to mention laws are passed with a future effective date all the time, especially when dealing with finances
According to this chart (shout out to @bean5302 for using the same competitive balance payroll figures that MLB is using to set their cap/floor proposals), if every team above the cap spent to the cap of $245.3MM and every team below the floor spent to the floor of $171.2MM, overall salaries would increase by 1%
For reference, salaries have been growing by an annual average of 6.4% since 2022 (chosen to eliminate COVID-related statistical noise) according to figures here and here
It's debatable what sort of indirect effects on market behavior would occur in that sort of floor/cap system, but the idea that salaries would increase by anything in the neighborhood of 40% is utterly absurd