This is kind of related to http://forum.simutrans.com/index.php?topic=10747.0, but extends way beyond the 19th century.
I've finally had the opportunity to try out transporting waste (no such industries have ever spawned for me before). The waste car introduced in 1890 does however have a top speed of just 75 km/h. This is lower than every other train car introduced at that time, and those with comparable (mostly higher) speeds get faster replacements later on. The waste car does not get any replacements, which makes waste trains a serious bottleneck even to other freight trains.
Waste is also very unprofitable compared to other goods. Trains need to be much longer than most other goods to break even, although it is light enough not to overload the locomotives like some other goods with low profitability. The somewhat older oil cars can carry more volume than the waste cars can. I would like it if waste cars got a bit higher capacity, even if that means increasing the cost to match. That would cause compatibility issues for existing games, though.
Maybe one can add a container car for modern waste too.
Perhaps. I have never seen waste containers, except for sawdust (https://jernbane.net/bo/subpage.php?s=3&t=8977) (another type (https://jernbane.net/bo/subpage.php?s=3&t=9016)). Then again, it is hard to tell what a lot of containers contain.