Unknown said:

And let me disagree with you. With much larger projects, it will be more useful, not less. The proof is simple, imagine I have this same problem but instead of having 8 files, I have 80... :-OOO

That's not a large project ;-)  Now imagine 6000 files in 500 subfolders.  How useful would it be in this scenario?

Unknown said:

I would better let users to judge the usefulness...

And indeed I did.

Having said that, it's not a bad idea for use when appropriate and I'd recommend you post this in the ideas site rather than here - http://ideas.sdl.com 

Unknown said:

In any other software, where you go to open files there are sorted by the OS

This reminds me of the DECADES-old BUG in Windows "Open File" dialog, where if you select multiple files the 'natural way' (i.e. clicking the first one and then Shift-clicking the last one), the last file is always placed FIRST in the list... :-(
The only way to retain the correct order of selected files is to highlight them using MOUSE and FROM LAST TO FIRST - only this way they are ordered correctly in the File Open dialog field (i.e. from the first to the last)... and subsequently processed in the correct order.

I told you the solution. You can do the same I am asking for the Files View in the Translation Memory section in Project Settings. See the Up and Down arrows within the red circle? I am only requesting the same in the Files View. This would allow an easy way of sorting files.

To get the task done is not a out-of-box functions in Trados. I think you can prepare two batch script to handle the files which need to be merged. Copy all your files to a temporary directory. And use the cmd tool if your system is Windows. And simply rename command will solve you problem. The syntax of this command is "Rename  sourcefilename targetfilename". But firstly you need to enter the files location. If you have hundreds of files. Use the pipeline command "dir >1.txt" to get the files name list. And copy the file list into an excel file. And  then construct your rename batch script in the excel table. You can easily get what you need. And rule of the rename list can be reversed easily. Of course, if using a software to do the work will be much easier. But it is more flexible of using the batch script, you can handle all  the action logic by yourself.

To get the task done is not a out-of-box functions in Trados. I think you can prepare two batch script to handle the files which need to be merged. Copy all your files to a temporary directory. And use the cmd tool if your system is Windows. And simply rename command will solve you problem. The syntax of this command is "Rename  sourcefilename targetfilename". But firstly you need to enter the files location. If you have hundreds of files. Use the pipeline command "dir >1.txt" to get the files name list. And copy the file list into an excel file. And  then construct your rename batch script in the excel table. You can easily get what you need. And rule of the rename list can be reversed easily. Of course, if using a software to do the work will be much easier. But it is more flexible of using the batch script, you can handle all  the action logic by yourself.