I do not think Meghans announcement had anything to do with the Brooksbank future baby. In fact once Princess Eugenie has her baby, the press will cover it as I am sure the Duke and Duchess of York will post images or comment. The papers will more than likely be cruel and mention that the baby's maternal grandfather has ties to Jeffrey Epstein etc...

I think Meghan's announcement was made for a few selfish reasons:
1. It is the "fad" now to talk about miscarriages ever since singer John Legend's wife Chrissy Teigen posted images of her in the delivery room after losing her baby on Instangram.

2. If the Sussexes were to be punished with the upcoming review, that will be put on the back burner, particularly if they were to be punished publicly as it would seem too cruel now as Megan suffered a miscarriage.

3. It could have a tie in to one of their proposed Netflix documentaries or programs about miscarriages etc.

4. It is to get Meghan attention and the publicity she craves, after all we know how much she loves attention.

I doubt this would have been kept quiet if the Sussexes were still in the royal family, remember that Zara Philip's also had a miscarriage and Buckingham Palace released a statement. Zara is further down the line of the succession than Harry is and does not have a title, so while the timing and reasons are more than likely selfish on Meghan's part it is not without precedent.