This would be another button new to the upload button we currently have, or a checkbox for "advanced mode".

This would first open a new "upload window" were the user can manually select what packages had changes and for the rest they would be able to manually input the file hash or pick it from an already released version, default will be the newer released version of the same visibility.

With this we can have more control to what is actually uploaded, potencially reducing nebula uploads due to incorrect uploading of packages that had no changes and save compressing time during uploads.

It would also have other options like selecting the number of parallel compressions (default 1 for 1.3) and concurrent uploads (default 1, max probably 2).