Will the game be x64 or only x86? If only x86 is there a particular reason why? If x86 can I modify the .exe to access greater than 2GB RAM (I have checked the exe already, its not set for that)? I have not understood why people have not moved to x64 from x86 yet much less dump XP (although I do admit to having a laptop with '95 still). I need to have a reason to own 12GB RAM 
I can’t really imagine Automation ever using more than say ~1000 MB of Ram. The current beta build uses 350 MB at max while having an engine on the test stand. Consider that for some reason triples when you have the economy part, the car designer, and the engine designer open at the same time, and you still are miles away from the 2GB limit. Don’t get me wrong, I actually pretty much despise non 64-bit software when it matters, including writing angry emails to to software firms that clearly don’t see the benefit of the 64-bit architecture… to no avail. 
Also, I have 32 GB of RAM, and my highest use has been 28GB so far.
At some point, if/when I have the free time, I may look at attempting to build a 64bit part. I would have to chat to Nortala as to how type safe the various pointer types are. I would be mainly doing this for the advantage in process architecture than RAM, as Killrob points out, Automation only uses around 350-500mb of ram so far.