1071565 update eu

This isn't done. A bunch of other things need fixing.

Posting this for feedback before I go do a lot of work that might get ditched.

feedback?
Every mapping type that we have, we'll have to specify the mapping keys that are lists of things. This is annoying. Plus it's problematic because if you add another list thing, it'll silently get turned into a singular thing unless you add an item to this list.

I'm not sure how to better specify that within the existing framework.

In the future, we can make building mappings much more intelligent where it can maintain the bookkeeping for us and "do the right thing".