Yes, it would be great to have source! The modding community does make up for this in some ways. For example, mods provide access to things like finding memory addresses for things like steering angle that weren't available in the API for game scriptors working on GTAV:

https://github.com/crosire/scripthookvdotnet/blob/dev_v3/sou...

re snow: It is possible to lay fresh snow anywhere in addition to drive through this area with snow burms, etc..

https://www.youtube.com/watch?v=rOo2mtuPkKQ&feature=youtu.be

Traction is definitely affected in snowy areas.

re tires bursting: it seems possible

https://github.com/crosire/scripthookvdotnet/blob/2b14a22ad3...