Hi Daniel,
EAG XML has not seen broad international adoption (though it has been implemented in some larger aggregators such as Archives Portal Europe) and more importantly, I'm not clear on whether or not it is still being maintained - the last update I can see is
from March 2015. So there are some reasons to hesitate in implementing it. That said, it is the only standardized exchange format for archival institutions, and it does follow ISDIAH, so support could likely be added to AtoM without changes to the archival institution entity in AtoM.
Primarily, this comes down to how we currently develop and maintain AtoM, which is described on our wiki here:
Essentially, while Artefactual dedicates time in each release to fix bugs, implement minor enhancements, update our documentation, prune unecessary code, and optimize features where we are able, we rely on community support for new feature development and other major changes. This can either be in the form of code contributions, or development sponsorship. If seeing EAG support in AtoM is a priority for you or your organization, and you would be interested in potentially sponsoring its development, please feel free to contact me off list and our team can prepare a development estimate for you. If you are, or have access to, a developer, we also have some resources to help get you started - I've rounded many of them up in this previous forum thread:
Cheers,