It is not really being sprung on them with how long it has existed. Not at all like continuing recording on a webcam where you might say things never intended for the party receiving it.

Are ppl who don't even know DKIM exists but know they have shady emails saved in the cloud or on their personal really just banking on repudiation and thats why they take no other action like deleting the email or putting more thought into emails they send? Seriously doubt it.

Exactly bc of statute of limitations, they would not have to look over their shoulders for the rest of their lives because of one poorly written email.