Is it possible for gohan to reach super saiyan 4?

According to DBGT, Gohan couldn't go super saiyan 4.

Because when Baby fused with Vegeta, they couldn't obtain the power.

You would to have the lights emitted of course, the tail, AND full saiyan blood. Which is why Goku and Vegeta have obtained it.

Gohan is 1/2 human making him impure and he wouldn't be able to go Super Saiyan 4.

Of course DBGT is not made by the same person. So one couldn't say.