I've got a Nexus 6p with a stretch fabric wallet attached to the back. This is great for storing credit cards since I don't carry a regular wallet, but it does make it difficult to pick a phone case, because the wallet already increases the overall thickness and many case designs don't have a flat enough surface to stick something to.
On the other hand, there are wallet cases that protect the phone, but all the ones I have seen open like a book to access the screen, which isn't acceptable for my work flow. A case that had a wallet in the back integrated into a dual layer shockproof plastic shell with nothing to obscure the screen would work. Or a case that only protected the four corners would probably work too, since this is all that is really required to protect the phone from being dropped onto onto a flat hard surface. Any kind of case that protected the phone without covering the back between the fingerprint sensor and the bottom strip would work too, as it would work with my existing wallet.