With Patch 10.1, Blizzard is adding a new reward for hitting Legend in Rated Solo Shuffle: a Pennant toy. According to datamining, this reward is also being retroactively added to Season 1, meaning players that achieve Legend: Dragonflight Season 1 will also receive a Crimson Legend's Pennant when Patch 10.1 launches.
This, however, hasn't been confirmed by Blizzard in any capacity, so it might not happen. Players interested in Toy collecting now have a new reason to play Rated Solo Shuffle from now on, as this will probably be a recurring reward for hitting Legend in future Seasons.
Win 100 Rated Solo Shuffle rounds while at Elite rank during Dragonflight Season 1. Read more on wowhead.com