My Dallas house has insulated hard metal ducts installed (since 2007) in the crawl-space under the floor. There is a central manifold where the percentage of air can be controlled from one central place. That sounds great, but I have not seen that central manifold because the crawl space is tight, and the metal ducts make it difficult to move around on the dirt. A small shovel is a good idea in order to trench under the ducts.
Having duct airflow control at a central place, and with remote control would be great.