I've had similar thoughts over the past few days, referring to it as a gutter instead of a tube. I don't see how it keeps the roots apart though, unless I separate and rotate them every day or so. I considered using half closed cylinders (imagine piece of pvc tube but capped, hole drilled in the center of the end caps, then cut in half over the length) of 5" length and diameter same as inside of the gutter. Both ends would be dammed, but with half a circle opening to overflow.
I used 5" so far. Surely 6" would give them some extra space but won't make 'the' difference especially when I place more plants over the same length of tube (nearly 4 feet, currently x 2).
I do like your setup, I do like the easy access. It's been a downside of my setup I overlooked from the start; can't check roots ones they got entirely entangled into a single mass not allowing me to lift plants. Do you still use velcro tape?
Easy root access could be the key though, at least to not spending tons on individual pieces. Easy access allows for more control, which you essentially do manually. I could perhaps add something to it, at least for those initial 4-5 weeks from seed (of which they are in dwc the first 2-3 weeks). So it's only for a few weeks really...
*from wiki hydroponics page. I used the same image before them to show what nasa uses for reflection (that ain't no white paint)
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Not exactly what I had in mind, the box would be roughly 3x3 instead and what seems to be the drain in the pic would be the supply, but would have multiple, and then drain at the other end. Similar to OPs setup but without all the supply spaghetti. The inside would have compartments that overflow near the side of the supply line, pushing/flowing the roots in the direction away from where the walls between compartments are low enough to overflow. Simply put, gutters in a box. The gutters hold the roots, the box is recirculated.