In the past I used WinRAR, but now would like to try DO, as I turned off the global context menu and don't want to press shift for unextracting archives.
I've noticed, that DO gives an error when selecting all parts of an archive. WinRAR notices that it already extracted the first part and ignores all following selected parts which belong to the archive.
Could that be added into DO, because I mostly extract different archive-files, select them all incl. parts and after extraction I just need to delete the selected files.
That's probably best handled by a script that looks at what you have selected, works out which files look like the first parts of the archives*, extracts them, then deletes all the parts.
I am not there isn't a safe way to do in general, which is one reason I'm weary of making it an official feature, but there may be good enough solutions you could put in a script if your archives come from a handful of sources and all follow one or two naming conventions. Multi-part archive naming is an absolute mess (especially the old-style RAR conventions, where .rar, .r00 and .r01 may all be the first part of an archive depending on who made it).
There are other technical reasons why it would be difficult to do this at a lower level, without adding the danger of unknowingly only partially extracting archives if the wrong part was selected, which I very much want to avoid. A high-level script tailored to your naming conventions makes more sense.