It is currently possible to add a virtual attribute to an entity, this value is calculated in a microflow when it's displayed and does indeed have the entity as an input. If you do heavy database calls in this microflow it could impact your performance though.
We're currently working on a major feature called Transient Objects where things like this are considerably easier. Objects then don't necessarily have to be stored in the database anymore to view them in a grid. That said, your exact request of adding an additional column with custom data is not part of this.
I did some testing using virtual attributes. Although it covers most of our requirements, it is very unfortunate that it is not possible to search or sort on virtual attributes or use them in a XPATH on the datagrid. This would be a very convenient feature.
It is nice though that virtual attributes can be used in microflows.