Does this matter? Corporations are on notice that this pendulum may swing the other way in four years (and remains permanently stuck the other way in certain states). They might just decide to steer clear of this minefield.
Ignoring all the other details, if someone waves the magic wand and makes it legal you can use it, when someone waves the magic wand and it's not legal, then the agreement is just void at that point. There's no retroactive consequences.
TFA notes that it may not have been declared legal. Rescinding a memo doesn't reverse existing case law; the meaning of said case law is subject to some disagreements (that the memo sought to clarify/remove).
Yeah I didn't want to go too far down the rabbit hole on the memo, just the most extreme case to demonstrate that if the law changes again, it's not a risk to the employer.
Nah, without the government to help defend against "frivilous" lawsuits by big corps, big corps won't be afraid to just sue the employees and make they pay the costs to defend or sue those hiring them to scare them from from employing them.
What minefield? They can have enforceable non-competes for at least the next 4 years. After that, maybe not, but it's so easy to include a non-compete clause into a new employee's paperwork that there's no reason not to do it, for companies that suck (that is, more or less all of them).
Even if they don't intend to go through the trouble to enforce them, they have a chilling effect.
Big companies already just ignore labor law and either hope litigation is too difficult for their employees or that the fines will be skimpy enough that it's worthwhile anyway.
Ignoring all the other details, if someone waves the magic wand and makes it legal you can use it, when someone waves the magic wand and it's not legal, then the agreement is just void at that point. There's no retroactive consequences.