Cars need better interface and usage of components. For starts, you guys could add high beams and different modes for lights based on the real car and how it works. Utilizing LED running lights, DRLs and hazards would add authenticity to street racing and for roleplayers (who are a massive part of the Forza Horizon community and Forza community in general). Another nice feature that would crush the competition is air suspension. Both aftermarket and factory equipped (on specific vehicles that have it in real life). Would definitely help with fitment and overall photography quality and it would be used quite a bit. And to move on from that, some cars have rev matching systems IRL such as the 370Z, 400Z (6MT), 6th generation Camaro SS/ZL1 models, both the GT350 and GT500 have it and R35 GTRs to name a few. Would love to have that for touring and cruising, it would be a great feature to have in a Horizon title. And last but not least, line lock systems. Aftermarket and factory, would definitely be nice to have that available when in launch control to get a better launch. Hopefully y’all can incorporate some of these features in FH5 or future Horizon and Motorsport titles.
Edit: Another nice feature would be HUD for cars that feature it IRL. Would be a massive game changer and with a wheel it would put the game on Assetto Corsa level.