These archive photos document the conversion of a Ficus benjamina to clay pebble hydroculture back in 2006. The tree had been growing in a Jardinier sub-irrigation (aka self-watering) planter.
I used a full force jet of water from a hose nozzle to remove the soil mix. I then pruned the root system so that the tree would fit into the homemade sub-irrigation planter on the right.
This took no more than ten minutes. The tree never dropped a leaf. Tell me about temperamental Ficus trees. These plants are tough and have very strong root systems if maintained properly.
I have done this many times. As you gain experience from washing the soil from other plant species, you will discover which have tough wiry roots and which are more tender. I would not do the full-force hose jet process on all plants.
My advice is to just do it! It's easy to learn. The root systems of plants are not as super-sensitive as many would lead you to believe.
This video taken of the plant wall installation at the Dodge Foundation headquarters shows a similar process. If you have doubts, the video should help to dispel them.