entity reference as attribute, is it possible in commerce v2? User story:
The end-users should be able to pick an image from an image gallery and attach that image to a product before adding it to cart

In Commerce v1 this was possible via line items by defining an entity reference field, along with a couple of other modules e.g. entityreference view widget. A sample, although not 100% finished, can be found in d7demo when you click on the 'add item' button.

I used entity reference since the images are actually nodes with a file field, so that i could also categorise them via term references.

Is the above functionality somehow possible on commerce v2? I cannot find  'line items' as used in v1, but only attributes and variants. However i cannot seem to find the way (configuration or contribs) to achieve the above functionality.

Any pointers to the above issue are very much appreciated.
Since product attributes are entities in CommerceV2, the following module should cover your needs => https://www.drupal.org/project/entity_browser

Some points to consider:


It is still in alpha
It is strongly supported at the moment by the community and especially the Drupal Media Team
It has more than 5K downloads.


There is also a recent presentation available from DrupalCon Dublin 2016 => https://www.youtube.com/watch?v=VXor-HZiYrs

Update: 
Following the documentation, you may also need to look into "Product Variations Fields", http://docs.drupalcommerce.org/v2/product/products.html.
This CV2 functionality seems to allow you to expose specific fields to the end-user for e.g. uploading images in order to modify/configure a product.

Good luck!