Time displaced Porthos looking for Revenge! (Perhaps he brings the tardigrade with him and perhaps they have some Red Matter...)
If they show Q on STD, bye bye STD. Nothing wrong with John de Lancie, but can we not stick him every Star Trek show. Can't we have a show that stands on it's own? It's not like STD is namedropping any existing STD lore... like Spock or Enterprise.... errr.... what was I saying? Bring on Q
In a classic case of literary "protagonist vs. self" conflict, the antagonist of the series will symbolically be the main characters' own hubris. Kor
De Lancie is a stud for a man of his years. Besides the gray hair and beard, he really doesn't look much older than he did at the end of Voyager, and he's such a strong actor, he could probably do almost anything. However, there's no reason to have Q on Discovery. I think it would hurt the show, and retroactively hurt/diminish the character in TNG/VOY. Verdict: Q-less is more