I would prefer recommending a stable build process: — a Docker image can be just like having a VM image or that one PC in the corner of the lab nobody is sure is unneeded. It's far better than having nothing or just the result file but it still has the possibility of needing to reverse-engineer the internal state and given how fast the Docker world moves I would not want to bet on format compatibility 5 years out.

Docker could be that stable build process but it requires the additional assertion that there wasn't, say, a truckload of changes made using `docker exec` or a bunch of customizations to files which were copied into the image. Simply putting a note on the source repo which says that might be enough.

(I really like what C Titus Brown has written about reproducibility in computation research over the years: http://ivory.idyll.org/blog/tag/reproducibility.html)