Hi Berthold,
the short version:
1) All files will continue to be accessible via wikivoyage-old.org. For how long only depends on Wikivoyage e.V. but Roland suggested multiple months would not be a problem.
2) Files need to be transferred by the community because - not all files may be eligible for Commons due to its licensing policies (freedom of panorama standards and other copyright specifics). Some files may be eligible under the new EDP that is being developed, but then they would have to be uploaded to the local wiki. - licensing and description templates as well as categories may need to be updated to work on Commons. - files should generally be checked for copyright issues, we need to sort out different standards and practices for things like email permissions to grant the rights to use an image, and so on.
Our legal department has strong reservations about a bulk transfer, and I have strong reservations from a community perspective. This is not just Wikivoyage being hosted by Wikimedia, this is Wikivoyage becoming a Wikimedia project. That means taking the time to do this properly.
Technically it is easy for anyone to do a bulk transfer. The reason this hasn't happened is precisely that people want to take the time to do it right.
If people are really worried about having red links, we can defer the migration date until more files have been transferred. Technically there's nothing forcing us to do it next week. Hans however will have greatly reduced availability after that and we currently depend on him to produce the database dumps.
It continues to be my recommendation to live with the red links at launch, and to just make it a priority to do the files migration through November. We can help with tools advice/support, and I would not underestimate the Wikimedia community's ability to pull this off.
Erik