There are limits to this: containers don't handle bulk cargoes (liquids, ores, grain, lumber), large assmemblies (automobiles, wind turbine components), or high-quantity gasses (e.g., LNG). There are some rail-based options for these (specialised cars), and in other cases alternate transport modes are required.
There's also the general problems that railroads are hard for many shippers (that is: entities looking to ship goods) to deal with, transit times are slow, and routing is inflexible.
There was an article a couple of days ago about Japan looking to implement a very long conveyer-belt system (<https://news.ycombinator.com/item?id=40809276>, <https://newatlas.com/transport/cargo-conveyor-auto-logistics...>), which is exciting if only that it's amongst the very few novel proposals I've seen in the freight world since intermodal / containerised freight became dominant in the 1970s and 80s. I'd be very interested in what a flexible end-to-end routing without major transshipment and switching congestion might look like. I still think steel-wheel-on-steel-rail is hard to beat for overall efficiency, but more dynamic management of trainsets, electrification, and the ability for, say, containers to autonomously achieve last-mile (or last 20-mile) delivery on their own might be game-changers.
In the early age of rail, one of the strongly-complementary transport technologies was horse-based drayage. The train could get your goods to the station, but further delivery within even a small town required a horse and wagon. In large cities such as New York, the situation was far greater. Automobiles and internal-combustion-engine based lorries utterly revolutionised this, and solved what was an increasingly intractable pollution problem of horse manure, urine, and corpses littering streets. ("Mud" is an interesting euphemism to look up, and fashion choices such as calf-high boots become far more understandable.)
It's also struck me that high-speed rail could (and perhaps should) revolutionise high-speed delivery, taking much of the demand off of air cargo especially for regional delivery. Old-school trains had post office cars in which mail was actively sorted en route. It seems that high-speed rail might offer an automated version of same possibly.