AmigoJack

That would be rather a convenient GUI feature: a target where you drop files without making up your mind how to pack it. But then again you could just start with your first file/selection (add to {new} archive) and then just drop additional files/folders to the now already existing archive opened in 7-Zip. You're even able to "edit" 7z files when it comes to creating new folders at any place (see the window menu).

The CRC-64 parameters 7-Zip is using isn't ECMA - as per https://reveng.sourceforge.io/crc-catalogue/17plus.htm#crc.cat.crc-64-xz that misidentification often happens and it's actually the XZ variant. The CRC-32 parameters 7-Zip is using are the same as used by PKZIP and XZ - as per https://reveng.sourceforge.io/crc-catalogue/17plus.htm#crc.cat.crc-32-iso-hdlc the variant is also named ISO-HDLC. I've been struggling with that too, as the correct CRC-64/ECMA-182 produces different results. https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Polynomial_representations_of_cyclic_redundancy_checks...

For now you have to decide to either have the format 7Z with all its advantages but without parity, or you could use the RAR format with not so high compression but supporting parity for decades already and maybe even more platforms than 7Z.

Welcome to the internet: it has absolute and relative URIs, and both are perfectly legal. Your web browser supports them, and you as a programmer need to support them, too. If you have a relative URI then you have to make it an absolute URI yourself. See Absolute vs relative URLs

Why would one need empty archives? Do you have 1-2 examples? Also: is it really "hard" or actually "impossible"?

Linking ticket: https://sourceforge.net/p/sevenzip/support-requests/409/

Welcome to the internet - please use links: https://sourceforge.net/p/sevenzip/discussion/45797/thread/dddbd68b23/

I already outlined that you might be unable to ever implement that yourself. Yet you wanted tests to then argued with cached read access. Yes: 7-Zip should not concentrate on this feature. It's already great to have RAR extracting support without needing the UNRAR.DLL. Not to mention dozens of other formats, too.