So I recently thought, if we will be playing as Locke for a good 2/5 of the campaign, we will probably see Chief doing some badass things in-game that we couldn’t do while we played as him. I think it would be a great opportunity to show what the Master Chief is capable of outside of cutscenes and books.
For example, you are playing as Locke, and you come across Chief in a campaign mission going beast mode on a group of enemies in a 5 vs 1, and he does moves on them like we see in the Halo 4 epilogue with the Spartan fighting a Brute chieftain. It would show what the Chief can really do being a Legendary Spartan-II.