Superko rules

This seems likely indeed. On written rules vs actual practice, it should be noted that written rules themselves are very recent. In the past people just played as they learnt (with tripe ko = draw or void game historically). And the rules were simple - truly, conceptually simple (unlike some modern inventions).

Btw, the idea that superko is a generalization of basic ko is itself dubious. Basic ko forbids immediate recapture, not the recreation of a certain position later. See here for a case where this matters (and where superko would prevent a non-perpetual repetition).

I can only guess but would be suprised if it would be ruled differently to a normal endgame ko + double ko seki (draw if actually played and neither side yields - so the bent4 player may choose not to start it).

Two useful links about the Chinese ko approach are the sensei’s page (a bit inaccurate as it forgot to mention moonshine), and the earlier version of written Chinese rules, with some hints hidden in the way it speaks about moonshine life at dia 3 and especially unbalanced repetition at dia 8.