For example, let’s say I wanted a map<string,int32> (or equivalent, just for example) - could I create that in blueprints? I know it’s trivial to do in code, but I just wanted to make sure I wasn’t missing something before heading down that route.
I just got a reply on reddit (the source of my question) from someone that appears to be involved with Epic. The answer is no. They will in the future be adding support for creating structs, and you can create arrays.
You can’t make custom structs yet, but it will be coming soon. I have been wanting this for a while too. 
You can make individual arrays of each type of asset though now. Just click the array button when making a variable. It is the little icon to the right on the Variable Type.
that will be a really nice feature, i am creating a separate blueprint with only vars to emulate a struct
Just to confirm as it’s been a while, is this feature already available in one of the latest builds?
you can make struct similarly like you do with blue print interface, however define one dynamically in another blueprint is infeasible. (think about the dependency hell it might have created).