Yes, you're right: the interfaces of the in-process adapter library have a few more evolutionary steps compared to the remote adapter libraries.
We do have the goal of unifying the interfaces in our roadmap, but at the moment we don't have a precise date for this update — and it's not planned for the short term.
If possible — that is, if the sets of item names handled by your data adapters are disjoint — you could distinguish them directly based on the item name.
Alternatively, you could have the client add a prefix or suffix that identifies the data adapter, and then strip it out in your getItems code.
Let us know if you need any further clarifications about one of these approaches.