If there's one feature missing from every train game ever made, it's subsidiary companies. In real life, in the US at least, it was extremely common for a larger railroad to create a smaller railroad to build and operate a particular section of their network.
As an example, the Union Pacific's primary mainline was from Omaha, Nebraska, to Salt Lake City, Utah: the original Transcontinental Railroad. However, UP execs also wanted access to Oregon and California. Rather than building the lines themselves, they set up subsidiary companies. The Oregon Short Line started in Granger, Wyoming, where it branched off of the main Union Pacific line, and built northwest to Huntington, Oregon, with the goal of Portland, Oregon. The Oregon Railway and Navigation Co already connected Huntington to Portland, so they simply bought a majority share in that line and reorganized it as the Oregon and Washington Railway and Navigation Co, which was a subsidiary of the Oregon Short Line, which was a subsidiary of the Union Pacific. The Los Angeles and Salt Lake connected the Union Pacific at Salt Lake City to Los Angeles. Together, the OWR&N, OSL, LA&SL, UP, and various other subsidiaries, were called the Union Pacific System. All painted their equipment the same way and lettered them Union Pacific, but somewhere on the car or engine would be small letters that showed which company the car actually belonged to.
Another great example is the Southern Pacific Lines. Everyone knows the Central Pacific, the pioneering railway that met the Union Pacific at the Golden Spike, but unlike the UP, the CP name wasn't the one they used for most of their life. The owners of the Central Pacific also owned the Southern Pacific, and they decided to paint all equipment on both railroads to match the latter. Over time, their system came to include many railroads, such as the Oregon and California, California and Oregon, Texas and New Orleans, St Louis Southerwestern (aka Cotton Belt), Arizona Eastern, Pacific Electric, Northwestern Pacific, the Galveston Harrison & San Antonio, San Diego & Arizona Eastern, and various others. This is why, until 1941, all rolling stock belonging to any of these companies was lettered "Southern Pacific Lines," because the Southern Pacific was actually a big conglomeration of many distinct railroads all working together and feeding each other. Here's a great image of a cab forward locomotive, the Southern Pacific's unique locomotive type, painted and labeled as a Southern Pacific engine, but sporting a tiny CP marking to show who it actually belongs to. https://c7.alamy.com/comp/KKJ0PD/southern-pacific-cab-forward-locomotive-4126-KKJ0PD.jpg
Anyway, sorry for the exposition dump, but how does this all relate to TT? Well, simply put, if I have an existing rail line, I may not want to simply build a branch, because I don't know if it will make me a profit or not, and after it gets mixed with everything else, it's hard to tell what budget items go where. However, if I can start a new company, and have that other company build the line, then I can simply look at that company to see if it's doing well, and see if I should formally absorb it or tear it down and try something else. Either way, it's no risk to the parent company because if the subsidiary goes bankrupt, all is not lost and it simply goes out of business, while the parent continues on like nothing happened. (Side note: the Infrastructure Sharing patch in JGRPP is pretty much required for this to be viable.)
This is easy to implement right now: just start a multiplayer game, and when you feel like it, quit and start a new company. If there are no other clients, you can switch between companies at will, making it easy to control both at once. However, there is one fatal flaw with this system: you can't fast forward at all. This seems like a trivial thing to add to single player mode: simply allow the player to take control of any company not already controlled by AI, and create a new company with a button. These features already exist in multiplayer and for spectators; all that needs to be done is to enable them in single player.
(I just realized that the cheat menu can be used for a similar effect, but it's kind of a pain to have to load your game into multiplayer, make a new company, and then go back to single player and switch using the cheat menu.)
Anyway, I could probably figure out a way to make this patch myself given enough time, but as a novice coder I'm sure there's someone out there who can do it much faster than I and save me a lot of trouble. So what do you say? Does this feature interest anyone else? Can someone quickly whip this up in the time it would take me to figure out what language I'm in, or should I do it myself?
Thanks for reading, and I hope this sparks some interesting discussion!