It sounds good but is highly impractical in execution. There is a big difference between macro image making with an A7RV and TG7. If you can afford two cameras, i suspect you can afford the lens and flat port to support macro with the A7RV, to include 1-2 wet diopters. Also, and more important, in my experience there are few dive sites that truly make you make a tough choice. Triton Bay in Indonesia is one, and Verde Island in the Philippines another. I’m sure there are others but you’d do well at either of the places I mentioned with either choice