@REDRA-11 I can already tell you air density is not going to make it into the game for EVERY track.. However we might get a different physics model for Mexico as that one has really special conditions..
Different car models wont happen. Not too many who want an outdated car model and Codemasters + FOM + teams dont want to have outdated models in the game. Everything needs to be licensed and there is always someone who doesnt want outdated things..
Alternative track layouts and more tracks are loved by everyone - for alternative layouts id choose pre 2010 Silverstone and MotoGP Catalunya - but its quite a lot of work and again a licensing problem, but its not 100% unlikely to ever happen again..
Just my thoughts on a few of the things.. In general though more depth, realism and variety is always great!