That would be a bit of a snub to Dominion players. Well, even more of a snub. Riot generally tries to retain the feel of champions through reworks. Although the champ obviously won't be exactly the same, high Mastery players will likely at least have something similar post-rework. On the other hand, there is nothing currently in League similar to League's gameplay. The replacement rotating queue might have Dominion-variants, but it's neither guaranteed nor always available.
A simple summoner icon was already an incredibly lackluster way to commemorate over four years of games. Repeating that process for champion reworks would further highlight Riot's flippant treatment of Dominion.