IMO, not even the President should be able to grant blanket pardons for any and all crimes that have not even been discovered yet.
This is going to come down to a matter of degree.
For example: The Ford pardon of Richard Nixon had a narrow focus and President Ford actually spoke to the nation to provide justification for his decision. I was mad about it back then but it seems quite reasonable in retrospect.
Counter example: Could President Trump, at 11:59 AM on 1/20/29, pardon “any and all members of the Republican Party, for any crimes committed at any time between their 18th birthday and this morning”? Of course not.
I have mixed feelings about attacking these pardons in the courts. But one thing is for sure - now that mass pardons for undiscovered crimes are a thing, a line is going to have to be drawn somewhere, somehow, by someone.