Cia used the gate of souls to travel to time and recruit the villains of that specific time. Because of this, the characters were able to exist all at the same time. After the events were over, Lana returned them back to their own time. The thing that would be a bit more tough is the Zant...
I don't think it's going to happen. Even though I personally think HW has a very interesting story behind it. I would love to see it become a part of the official timeline but that's never ever going to happen. To be honest ity would be very confusing because where would they even put it? But...