Just watching the stream on Mixer while signed in will offer quests and unlock certain in-game FM7 gear, including the ForzaRWC driver suit and matching car livery, the five liveries from the Driving the Design artist series and (what else?) a Unicorn livery. If you’d rather watch on Twitch instead of Microsoft’s Mixer, there’s a special extension that can provide game rewards.
Microsoft and Turn 10 started the Forza series in 2016 when digital motorsports were starting to take off, but the 2018 season is coming to a close in a fundamentally different landscape. Now, it’s not unheard of to see pro F1 drivers and car manufacturers with official esports teams. They see this as a big opportunity to promote both themselves and motorsports in general, and high-profile events like this might just reinforce their opinion.