Huh...I really thought Super Saiyan just completely overwrote Kaioken. It makes no sense that Goku wouldn't have used it before now if that wasn't the case. I mean, yeah, they said it damages his body. But he's been in quite a few situations where Earth or the entire galaxy have been at stake should he lose. And he's always just scraped by, when he apparently could have just Kaiokenned instead.
That said, the episode was still awesome and Hit is the goddamn coolest.
Himself decades ago?
This is functionally the same as the Other World Tournament. Escalating it to "universes" is a meaningless distinction, because they're all still just aliens.
That accusation ignores the fact that it was the obvious choice in the first place. When your main character is the strongest character in the universe, the next logical step is other universes.
It's like a fanfic creating a Super Saiyan 5, and then accusing him of stealing the idea later if he adds a Super Saiyan 5.