From what attorneys said online, the best action is "Wait and See". What the May 21 memo mentioned will pose a lot of question marks due to lacking clarity and also will invite a substantial number of lawsuits. The content of the memo reiterates the text of the law, but doesn't change it at all. If such memo is challenged in court (and I believe it will be), there is a BIG chance that a judge will strike it down. The best rational step to be taken right now is waiting, consult with an expert attorney about one's specific case if necessary and follow their advice.

yes all applications without approval are subjected to the rules under the memo, no one is grandfathered in. K visas are exempt

according to the memo effective immediately