I find it odd that if you're going to place Krypton 27 light years from Earth, why create a permanent wormhole in order to, in effect, place it right next door? Why not just have Krypton be right next door in the first place - planet 12, or the former asteroid belt or something. Originally, it was Krypton that died (from "old age"), not its sun. And the color of the sun was no factor in Kryptonians having super-powers. So Krypton could have been right here in this solar system with no conflict. That way you have all the Kryptonite you want, and the space journeys could have been done with traditional rockets in a manageable time; consistent with Krypton's anti-rocketry history.
I thought this was the original logic on Krypton's location - that is was the asteroid belt before it became the belt - on the way back 1940's. I just laugh when I see this topic - do you have any idea how much time in science class I used trying to figure out the scientific angles to super-powers?
I think placing Krypton out in the nether-realms past Pluto makes the most sense. Then it's not too close, but the occasional mysterious object (like Kryptonite meteors) can swing in close to Earth, then back out on their long, elliptical orbits.
Sounds a bit like a story that's being produced here. Hmmm...