Johnson knew what the ladies liked and he was certainly old enough to have a son the right age that could be similar, but not a carbon copy of his character. The original Johnson was just a one-note stereotype from Aliens. Junior could be more nuanced. Or not. With Buck now a Spartan, there isn't a hardened veteran Marine/ODST character. If someone asked who is the most badass character in Halo, many people would answer Johnson(even if he kept getting captured in the games).
Halo hasn't been afraid of introducing children of established characters with Miranda Keyes and Rion Forge. However, those were both opposite-sex children who were much different than their fathers. The Johnson legacy is just a memory, and there are probably some Halo players who haven't played the original trilogy and have never heard of the name.
In Silent Storm, Johnson was a mentor to Chief. It would be poetry to have Chief mentor a recently promoted and cocky Johnson Jr. If done correctly, it can be respectful to the original character while filling a hole in Halo left by his death.