i just dont like the idea of bending a plant that low ive been getting that responce alot and it makes me wonder why no ones every tried to disentangle a rootball if tangling prevents growth? i do like your ideal i was thinking mesh would probly keep the soil from draining down but not completely....you should try a layer of leaves or...pebbles...what kin da median are you thinking of using on the hydro half that greatly influences whether soil can leak down along with the roots and moisture....you would have a nasty resevoir no matter what but that dousnt really matter unless you want to cycle it.at least your way yoiu dont abuse the plant at all.
i don't think the soil would drain down. when i fill a new 4" pot with soil to germ i really soak it down so everything settles, let it dry out for a couple days then plant. never had stuff come out the bottom.
maybe it should be stacked 3 deep like this:
4" drilled germ pot, with soil.
4" pebble or hydroton pot with lots of drill holes, kind of like a net pot.
hydro tank with airstone.
that sounds like a decent hybrid system??
as far as untangling roots, weed roots don't need to be untangled really. they will get bunched up and twist all over each other but it's not bad as long as they get what they need for their short lives. a tree or something is a different story because they keep growing so long.
.