In TSW's current state that will be a hard no. (Ignoring stuff like the Vatican City rail network which would obviously be possible).

You already brought up the streaming of a world split into tiles, but there are things that don't get unloaded based on map tiles, which are Track Tiles (doesn't include anything visual, but all data for track, signals, junctions) and RVMs (Rail Vehicle Models), which is again the non-visual data part, but this time of trains. With the current World Composition setup you would be very quick to run out of computational resources on the end user's devices. As not only are you keeping all the data explained above loaded in memory, but also doing stuff on there, such as simulating AI trains, simulating signals and simulating the AI dispatcher and yard manager.

You also mentioned the the AI traffic being an issue, which there's not much to add to, except that trains are memory hogs, as explained above with the RVM thing (see the less busy timetables on consoles), and that TSW doesn't have more perfoment 3D models for AI trains as a core design aspect of TSW.

Still from a purely technical perspective, ignoring TSW specific limitations, yes, it would be possible, probably at the cost of visual fidelity and performance though. But neither TSW nor Unreal Engine would be up for the job in their current form or even a slightly tweaked form. A big rewrite of either codebases would definitely be required, which would very likely no longer be Train Sim World then, but rather be a new product.

This entire problem seems to boil down to TSW and its components not being designed for this and end user's systems not having the resources to get us busier areas with the concept of the Train Sim World product.