Route's
I highly disagree with poster who said to leave America alone. You're talking about a huge market and a huge rail fan area....also you're talking about some of the most scenic routes to be found anywhere. However so far the scenic routes in America haven't even been scratched. Instead they do the most flat areas possible for ease of creation.....
Example one of the more Awe inspiring rail lines to me is the Natural Tunnel State park line. They used an actual large cave for a large bit of tunnel, It's kinda like Train Spelunking....
http://youtu.be/0p2C4-VtYvc
Sadly I have never seen video from cab actually going through it, maybe a developer could convince NS to allow a ride along....From what I have heard thanks to recent changes you'd get further with them I'd wager then with CSX, as they are more railfan friendly thanks to old Southern staff coming to power.
Also the Alaska Railway, simply among the most gorgeous scenery on any line, and still goes through TRUE wilderness, would be great to incorporate wildlife....etc Will NOT be for those that fear difficult Terrain....
Alaska Railroad
http://youtu.be/uBiLbfdKweI
http://youtu.be/gtjdGyBuanE
White Pass & Yukon....America's Albula...
http://youtu.be/XQoeAekFQMI
http://youtu.be/CVrmsGEY0Dg
Honestly someone could do nothing BUT Alaska routes and have eager followers for years.....there's so many, and unlike the rest of America it's still a major area for passenger rail...as many areas are only accessible by railroad or plane.
Likewise Canada's Rocky Mountaineer
http://youtu.be/VXxgRlIoEgg
Chicago's Metra System is honestly more interesting then North Eastern Corridor expansion...
http://youtu.be/UvayIEyHkOE
Chicago really has endless possibilities for die hard freight fans, this city is train CHAOS!!!!! They used to have a deal where every major rail line had to end at Chicago, and as a result trains crossing the country are get bogged down there....it is a shunting nightmare. Also one of the busiest hump yards.....I doubt a hump yard can be simed though with any current engine. I highly recommend watching the great HD series "America Revealed" on transportation for this part, they spend a bit of time talking about issues in Chicago.
Also getting away from Chicago on Amtrak's Empire Builder to Washington has many neat sections
http://youtu.be/jss6BEvOgtw
Cascades would be epic....especially if you could sim snow plow action. There is no range on earth that snows as much as cascades they take plowing to a new level....
Highest cog railway on earth is on Pike's Peak......again similar to Swiss and Austrian rail...
http://youtu.be/hPjL5P-j4vE
What we need more of everywhere is Narrow Gauge......
The Rio Grande's Narrow gauge lines are epic....
http://drgw.free.fr/DRGW/DRGW_en.htm
Likewise while we have an excellent community route of Albula there is not a single piece of narrow gauge Rhb stock....I desperately would like to buy a Swiss Crocodile that articulates some, or really I like nostalgia the yellow ABe 4/4 Summer cars would be very cool.
1000m narrow is in high demand.....because of the beautiful albula rte....so far we got nada...
I think Austria is FULL of great narrow gauge lines I would love to drive.....
Great info on them on this video (which I highly recommend getting the full one it's on Amazon instant. )
http://youtu.be/qTLlCSnid-k
I would also like to go back in time and do some classic streamline trains
Burlington Zephyr 1934 - High Speed Streamlined Train in America
http://youtu.be/HXZMMVz6lY8
There's lots of "classic" possibilities. Someday I'd like to for a revamp of Chattanooga area where I live, and show the original stations like the old Union Station now torn down, and put in all the old trolly streetcar trams including the one that used to go up lookout mountain .
http://railga.com/oddend/streetrail/chattanoogastr.html
For that matter I would just like more trolley's and streetcar tram lines in general...
I also agree that JAPAN is in desperate need of some routes, and they have some of the most die hard railfans anywhere.
China would be cool, I love China Rail as you can still really take over night trains and long journeys everywhere..... India is famous as well..... the Trans-Siberian train from China also has alot of great segments.
Really for me half the fun is exploring interesting terrain. I would be happy with some wild and crazy fantasy routes have fun with it....anyway just my thoughts...