Something I think FH is lacking, is OEM car parts when customising your car - we get one standard basic spec and on a few cars there’s options for some OEM body parts. wing, bumper, rear bumper etc.
What I think would take Horizon to the next level is really speaking with Manufactures and implementing more customisation with OEM parts so, as example when you spec your car in real life, you have options on different manufacture rims, you have a carbon ceramic brake upgrade with OEM callipers (Not the very outdated basic looking brake upgrade) you can choose interior trim. Other games have implemented this and it enables the player to really design their dream car in the spec they image it.
in short
-More OEM rim selection
-Brake upgrades to use OEM Carbon Ceramic option or steel option instead of basic outdated look now
-More OEM body Parts
-Interior trim selection