Manually keeping autoloader class names up to date time consuming and unnecessary burden. Additionally it bloats extensions.json which can get thousands of lines long. Replacing the autoloader section with simple PSR-4 declaration makes it shorter.
Slightly more complicated is to not break other code using Translate's classes, mainly TranslateSVG and CentralNotice come to my mind.
The initial plan for namespace structure is documented in https://www.mediawiki.org/wiki/Extension:Translate/Namespaces