Nice list, Mika.
Think of the bright side. MW has a much higher poly limit, but much less usable cars compared to HS.
HS also "will" work with modern pads like Xbox 360 controllers. It's effectively plug and play. It plays pretty well with them, too, but since the game came out long before XInput was a thing you get no vibration unfortunately.
One thing I'd like to do is make upgrade for "classic" addon cars. It's not really that hard to change small stuff. There are people who mod higher detail games who make pretty convincing racecars out of street models with little if any modelling. An old pastime of mine was also to make "accurate" performance. I've spent countless hours searching for info on the web. Cars like Maserati 3200 GT were pretty hard to find data for because they were sold in small volume and probably restricted to Euro market. Today however you have many owner clubs for many different cars so you can just ask. Porsche and Ferrari are privileged because of Rennlist and FerrariChat.
noise spoke of source code release, that would be great but it has no chance of happening because of how EA is. Source code release, despite Doom and Quake's success, is pretty unique thing. John Carmack is a guy from different times, he had a completely different mindset from the big corporations of today. Most of the games Carmack either had the rights to or was involved in had their sources released. Doom's everlasting impact is thanks to his vision of open source.