Just saw this, so will answer now as a reference for future searches.
Yes, you can create new types of entities in AEP now. The concept is
called "multi-entity segmentation", and as you describe this allows you
to create lookup data that can be tied to both XDM Profile schemas and
also XDM Experience Event schemas for things like product lookup, zip
code lookup, etc. These fields can then be included in the segmentation
logic boolean expressions same as your profile and event attributes. The