The successor of the Mackensen class BCs was the Ersatz Yorck class. Its first member was the 'Karl der Grosse' and she was commissioned in dec. 1920. She was the first battlecruiser to carry 15" guns to counter the british Admiral-class. The british admiralty wasn't amused when they got reports the german 15" gun was able to fire, reload and fire again within 23 seconds. 1.5 times faster than its british counterpart. 'Karl der Grosse' was the last battleship or battlecruiser for the german navy for the next 10 years. The following class was the Scharnhorst class.
Size 38000 tons full, 228m/747" length, 8x15", 12x5.9", 8x8,8cm aa, 3x60cm torps tubes
This is her look at commissioning in 1920.
In reality for three ships of this class were keels were layed. At the 1918 armistice there was an estimated building time of 26 months to go. They were scrapped.