Goten!!! I plant as much of my tomato seedling underground as I can either straight down or by using a trench and training the tip back up. The result is huge root structures due to tomaters having stems covered with initial/primordial roots. That's tomato 101.I have not tried it with weed as the basic rule of thumb for most plants of any species is to NEVER cover the stem with dirt or mulch due to rotting issues.
Have you ever tried planting deeply even if the seedling were not leggy
Does it work with hardwood stem as well as softwood. Do you think if I plucked all the leaves and stems off a say 15 inch plant except the terminal node the plant would develop roots along it's entire length??
If it works as well as you say (and I sure have no reason to doubt) then the potential is huge. To get roots down deeply early in the season outdoors would just keep them down with all the moisture when the summer temps take off and would make much better use of watering.
I have not had a crop since 1984 but the kids are gone and I can dive back in.
I can't plant indoors quite yet but I might try testing your idea. It's slicker than snot on glass my friend. I am gonna go smoke a bone turn the compost pile and contemplate this.