It's 2020 and I know the question was asked a long time ago.
We like to use the rpi for an industry application (process monitoring)
Nobody can stop you from doing so, there might be better but also worse alternatives depending on the task at hand. As for the questions:
1. power supply from 24-48 volt
Search: "din rail dc power 5V" (you don't want to convert power multiple times)
2. powerdown mechanism to protect data from an outage (safe automatic shutdown with battery or condensator when there is an outage)
If the raspberry pi is mounted inside a cabinet with a main switch and you want to use it to also power the Raspi on/off safely, you could build a circuit that takes advantage of overlays:
In this example pulling GPIO pin 21 to low causes a shutdown and after the shutdown GPIO pin 20 goes to high (I'm not an electrical engineer so I removed the circuit posted here previously).
Another option is to set the file system to read only which is easily done in the latest OS using the GUI of the Raspberry Pi Configuration: Performance/ Overlay File System.
For dealing with (potentially homemade) problems resulting in a hang (memory leaks and the like) you could take a look at the built in Watchdog feature.
3. housing for rpi and power supply mountable on a din rail
Search: "din rail raspberry pi", there are plenty of boxes / housings to choose from.
Is there such a packaged solution on the market today?
As for the powerdown mechanism there is a lot out there but I didn't find anything ideal yet (at least not for me). Some don't completely cut power resulting in the Raspi not booting up again, some use Lithium batteries that I don't want, the energy stores tend to degrade over time a.s.o...
For a recent din rail mounted project I simply use a read only OS file system together with a dedicated ext4 partition for an sqlite database file How To Corrupt An SQLite Database File.