That's a really cool technique DJtommy! Very innovative thinking by Kimura for back in the day and I think he's the first to do this. I believe there are positives and negatives to it and i'm not sure how frequently Japanese Professionals still use it. The positives are that it's much faster to get the tree into a Bonsai Pot. The negatives are that you'll always be left with a long portion of live vein that does not produce roots directly off the live vein, more root and vein mass and it's likely more challenging to re-pot the tree. Now it's been replaced mostly by grafting roots onto the live vein and eventually removing the lower portion of the tree all together. There's a great section written about this in the book by Takeo Kawabe one of Kimura's former apprentices. In the US, Boon Manakitivipart has done fantastic work with root grafting as well.
Here's a couple pictures of root grafting taken from Bill Valavanis's Blog during one of his trips to Kimura's garden in 2014.