IMO, it's much easier to have a staggered harvest if you grow in soil.

With soil, you can put blocks under the newer smaller plants to get them up to height with the older plants to make an even canopy.

With hydro, the new plants you bring in will be too far from the light and will stretch up a lot to reach for the light.

I guess there are other reasons too why you wouldn't want to do this with hydro.... plants will need diff nute solutions depending on what stage of flowering you are in. It would be pretty hard to be flushing some plants while other plants are just starting to bud up if they are in the same hydro system.