That would require trainings of the respective translators. While I don't know, if translation agencies are open for this at all due to their internal workflows (might depend) some other points are:

• Texts might be subject to a blocking period before published (which would require externals to have access to collab, putting the workload to move the translations again on the team)
• Translators for translation agencies are not always the same persons.
• Texts translated by translation agencies are not always ready for publication, but need a review and some corrections first.

Addendum: plenty of teams at WMF and even chapters are frequently working with translations from translation agencies and external translators and have to publish them on Meta. Importing these by such a script will probably help them all to save a significant amount of time. I assume, it would be very helpful to create that interface soon in a second step.

Movement Strategy and Governance is maintaining a termbase of about 600 wikispecific lexemes and their translations in 16 languages, soon to be about 25 languages. This internal resource is supposed to be shared with the movement on Meta soon, but to make it editable by using the translation extension and to enable future growth in any direction, we want to export it, which is yet not possible. This script would help a lot in sharing.