Even at that, Judge Cannon's order to the parties is a routine pre-trial step. What Smith dislikes is that it hints at preservation of the Presidential Records Act as an issue of fact for the jury. What Smith wants is for no such defense to be available for Trump. How would an appellate court panel rule on such a claim?
Who knows, but they would have to take up the issue in detail, with Trump able to present his side and then have potential en banc and Supreme Court review if the decision went against him. Smith knows that he has been outplayed and that the documents case is unlikely to go to trial before the election.
If any valid legal defense exists then Trump has a right for the jury to consider it.
I agree an interlocutory appeal would delay things, not clear exactly how long.
Smith is running out of time on this one.