Ulrich: From what I can gather, the Seydlitz was built in Bremen, not Kiel where GZ was. I thought it might be the first M-Class cruiser from the "Z Plan", but the info I found states that work on those ships was not started until November 1938. At best, the shipyard workers would have only had a month to lay down the hull of what we see in the photo -- not likely, IMHO.
Here's my off-the-wall guess: it's the Franken, an auxiliary ship. It's the only ship I could find that was laid down in Deutsche Werks Kiel (in 1937), launched after GZ, (March 8th, 1939), and has a similar bow shape to the one we see in the picture. Sadly, I was unable to find any photos of Franken, so I cannot be 100% certain.
Karl: You raise a good point about C2 of the aircraft on GZ. I was simply suggesting how coordination and command of said aircraft could
be done. Given Ulrich's mention of Göring's complete control of the Luftwaffe, I think the first "step" in a possible evolution of a KM air arm would have been some sort of liaison officer from the Luftwaffe to control (yes, I said control) the aircraft on the GZ. As you stated, it probably wouldn't have been too efficient (maybe even disastrous!), and if given enough time to evolve, perhaps the KM would have adopted the approach the USN and RN developed.
Of course, if Göring refused to allow "his aircraft" onto the GZ, perhaps the KM would have considered using the GZ as a "floating decoy". I can imagine cardboard airplanes and such like the Allies did with D-Day and Patton's "army"
I'm not saying it would accomplish anything. Seems to me that the GZ was destined to fail unless it could sortie with more than one carrier as part of a battle group. Had the KM not stopped construction of her, perhaps she could have sailed with Bismarck and Prinz Eugen as part of Operation Rheinübung.
Sorry, didn't mean to conjecture so much, just wondering what could have happened....