Given that Raisa seems to be handing William his Flash-themed backpack, we may discover that she will have a hand in raising William on a regular basis.
It’s a sign that Oliver is still fond of Raisa that we see her in a photo with William.
Raisa could be a valuable resource for him, both as somebody he trusts and somebody who presumably knows something about raising young boys.
Whether this is because Samantha died in the Lian Yu explosion or Oliver needs help whenever he might get custody of William remains to be seen.