Maybe its like a 1v1 race mode that you sign up for like The Trial. You get put in a race against someone else - either on-road or off-road, maybe the routes are auto generated like the Eliminator.
Each race completed adds a total to the tally of "finished race-off's" by the community. Looks like there is a meter for Asphalt and Off-Road, so perhaps there is a certain number the community needs to accomplish and we'll get a reward for both.
Anyway, we'll soon find out what the race-off is all about. In the meantime, here is a speculative list of vehicles I think would suit the theme of the update.
Asphalt Racers:
From past Forzas:
1960 Aston Martin DB4 GT Zagato
1948 Ferrari 166 Inter Sport
2011 Lotus Evora S
1961 Maserati Tipo 61 Birdcage
1957 Maserati 300 S
2021 McLaren Sabre
1980 Porsche 924 Carrera GTS
1960 Porsche Emory Motorsports 356 RSR
1963 Shelby Monaco King Cobra
2004 Vauxhall VX220
2018 Volkswagen #94 VW Motorsport I.D R Pikes Peak
New to Forza:
2020 Bugatti Bolide
2020 Koenigsegg Gemera
2023 Ferrari Daytona SP3
2020 Maserati MC20 Coupe (will it ever come?)
2023 Pagani Utopia
2023 Porsche 911 GT3 RS (992)
Off-Road Racers:
From past Forzas:
2018 Alfa Romeo Stelvio Quadrifoglio
1974 Hoonigan Ford Bronco
2006 HUMMER H1 Alpha Open Top
1991 Jeep Grand Wagoneer
2008 Volkswagen Touraeg R50
New to Forza:
2024 Jeep Wrangler Rubicon
2022 Lamborghini Huracán Sterrato
2022 Maserati Levante Trofeo
2023 RAM TRX 1500
2023 Porsche 911 Dakar Edition
2017 Subaru Crosstrek Desert Racer
Will we ever see the Crosstrek come to Horizon? I think it would be the perfect fit for this update