Given an opportunity like that, here's what I will do:
1. A film that would be at least 2 hours max or shorter.
2. Big G's screentime should be sufficient, perhaps as long as his hensei appearances. All the suspense and "keeping in the dark" is the job for trailers.
3. I will keep another kaiju a secret. Godzilla's trademark is a monster rumble, so that is part of the plan, but a surprise to the audience. A classic opponent will be used. Perhaps there will be another kaiju who cameos as a victim of either. I'm thinking Manda corpse floating on the ocean.
5. He will use an atomic breath. He will use it in full effect which will include buildings, tanks, jets and against another monster. Of course, same drill: glowing spines, blue beam, destruction!
6. This Godzilla will be an anti-hero, he will destroy a bigger threat but everyone should get out of the way. He will also be back to his atomic mutation roots.
7. The main theme would be the environment once again, however, both Godzilla and his opponent will be both similar and different. They are both products of man's recklessness with mother nature and science but different circumstances were the reason they came about. Godzilla from radiation, the opponent maybe an abberation from genetic experiments and hazardous wastes.
And lastly,
8. I wanted it to be a one and done film. Maybe similar to GvsD, where both kaiju dies but you know there is nothing else afterwards.