First: From what I see the game looks great and I preordered it. Great stuff! It was more than time for another decent train game!
A very interesting topic seems to be the map size. Of course bigger means better here. Being a cross platform developer pro myself I’m curious about the reasons for the map size limit.
Is the reason for the map size limit the memory consumption or is it execution speed?
If it is memory usage there should be no limit if the software runs on 64 bit – your installed RAM is the limit here. Only 32 bit Windows (which is used essentially on old Windows machines, does any gamer still have 32bit?) would be have a real limit here. So: are you planning a 64 bit windows version? I assume that the mac version will be 64 bit anyway.
If the reason is computation time then another question is: how do your algorithms scale? If they scale linearily with map size then you should think about relaxing the limit for more powerful machines. This also depends on how good things can be parallelized. The more parallelism is possible the more you could relax the limit – eg. an eight core AMD CPU or Intel i7 would be 4 times faster than your system reqs. I would like to use that power.
If your algorithm is very parallelizable you could even run it on the graphics card (using eg. openCL). This would give you more power than you need. (100 times faster than on a single core computer is realistic here.)
If the algorithms scale quadratic however, you’ve got a problem.
Would it be a problem if a map runs on one machine and not another just because one machine is more powerful than the other? I think not. A great game was always a reason for upgrading my PC! I’m strongly agains punishing people with decent computers for the sake of low system requirements.