I stumbled across the Railroad Tycoon 2 untold strategies document again and noticed there was a wishlist section at the bottom much like this thread, with an additional list of things the author thought were not good ideas. Personally, I think most of them could be implemented in modified forms, with the option to turn them all off and play a purist game for those who want to:
Tunnels would be a nice QOL feature, but it's definitely true that having hundred-mile long tunnels would be unrealistic. Tunnel lengths could be severely restricted to address this, with longer (but still reasonable) tunnel lengths possible in the 20th/21st centuries. Maximum tunnel lengths could be an editable scenario/mission property to reflect the different scales between maps.
The max train length could be shortened in the early 19th century, and gradually lengthened over the course of time. Spitballing one possible implementation: 3 car maximum in the earliest years, 4 cars max before the 1850s, 5 cars max from then until the 1900s or 1910s, 6 cars max until the '40s or '50s, 7 or even 8 cars max in the late 20th century and on. It would certainly depict the increased hauling power of locomotives over time. However it might also interfere with the difficulty of "loads hauled" goals for scenarios/campaign missions.
Adding two engines on one train might add a little complexity, but I think it could be a viable option once electric locos are established and beefier diesels come out in the mid 20th century (the option would not be available for steam locos). It would increase speed a bit and increase traction a lot, making steep grades less of a problem, but it would take up a train slot meaning you'd be sacrificing a cargo car. The F3A+B is basically this but in the form of a single discrete locomotive, so perhaps the option could become available for subsequent diesel and electric engines.
I fully agree that making the player carry empty cars back to their origin is a dumb idea, so I have no suggestions here. RT2 doesn't reach that level of granularity.
My own humble suggestions would be:
Add freight/switching yards as station buildings to increase turnaround and overall efficiency. The whole station upgrade screen would probably need some QOL/overhaul work put into it for any hypothetical OpenRT2 though.
UI and in-game menu graphics changing to reflect what era the player is in, eg. the stock market screen going digital in the '90s. The 19th century style still looks good but it's not exactly fitting for scenarios set in, say, the 1990s. This is an art project more than it is a development thing though, so YMMV. The game's bluegrass music while excellent has the same, er, issue, but I usually just listen to external music in those cases.
