Carlson has hit LHP a lot better (.757 OPS) than RHP in his career, he could possibly play in RF sometimes vs LHP with Seiya DH'ing, especially if Shaw is scuffling. Conforto probably won't get much playing time when Seiya is back and everyone is healthy, he's blocked everywhere and he'd be on the team as insurance in case of injury somewhere or Mo scuffles.
I can't see Kingery ever getting a start even if an INF lands on the IL. He'd be a PR and riding the bench in case of mid-game injury. I think Shaw as the only backup INF is fine as long as they never start him at DH, which would be easy since he can move around and give regulars some rest at DH vs LHP.
However, but it would be nice to have a good PR in the 9th for Mo and Kelly/Amaya. Carlson only has average speed.