What happen to Goku when he went in shenron?

When Shenron took Goku away into the sky at the end of Dragon Ball GT. No one Really knows what happened to Goku. My theory is that Shenron took Goku away because he was the strongest being(except for Shenron) alive. Shenron fused the dragon balls with goku for immortality so when Goku was needed again, pretend in a hundred years, he'll still be alive. But if you ask me, Dragon ball GT is really lame. Enemies like Freeza, Cell, and Majin Buu(From Dragon Ball Z) is something way better than Baby, Super 17, and Evil Shenron.