I think the biggest factor is still going to be whether Tatum has another level of efficiency he can reach and being able to score in the halfcourt consistently. Then the second biggest is whether Porzingis can stay healthy for an entire playoff series and physically hold up against guys like Adebayo, Embiid, Giannis, and Jokic.
That being said, there were definitely playoff games where I said to myself, if Marcus could hit the open three more regularly this game would be over. The defenses were always designed to tempt him to take the shot, and that will be a less effective strategy with Holiday there. I know Holiday has had his bad shooting games in the playoffs as well, but his catch-and-shoot numbers suggest he should be better in that spot.