Thanks for the comments.
Concerning IPTC: I suggest to use configurable properties and provide a default configuration for IPTC properties (perhaps not all, but common ones). Probably there should be mapping options in configuration to allow for automatic import.
Probably just referencing a node is indeed quite easy. Although dimension handling might be a bit difficult (at least concerning UI). We could start with using nodes as meta data storage and improve the functionality afterwards (use the node tree for a tree based asset navigation for example).
But thinking of the tree based navigation: It could make sense to use the CR as the basis and reference the assets from the nodes. Adding a reference to a node in the asset model would introduce a dependency to TYPO3CR in the media package. That could be a problem for those who use it in a Flow application without Neos.
So I propose to follow the RFC of @dfeyer (merge media module in Neos) so we can use nodes as a basis and reference the media assets from the nodes without creating a dependency to TYPO3CR in the media package. Sounds quite complex, though, if you think about the implications (tags, asset collections…).