I'll admit, right off the bat that this takedown looks a little 'martial artsy'. I mean no one is going to let you step behind them right? Especially after executing a rising block like in Do-San...Yes?
Well no, actually wrong! Cus stuff happens! people find themselves in all sorts of positions when negotiating violence. It's a hap hazard chaotic process as you never know what the guy is going to do, so you never know how you might need to respond and from where.
When training such techniques you should concentrate on the principles. As Itosu said, to paraphrase
"the techniques may vary, but the principles never do...they remain constant".
Attacking someones centre of gravity when crouching below them may seem far fetched when one is in a white suit and training in a school hall but change the context and it becomes a bread and butter principle.
Indeed attacking balance by crouching lower than your opponent is the standard method of wrestling (and I don't mean WWF) takedowns. It is also the most common method of balance displacement in modern MMA.
Traditional versions of most techniques tend to be a little less refined than those of combat athletes. The reason is that they were never meant to be used against those with knowledge, but rather they worked best against those who had NO PREVIOUS knowledge of the technique.
THIS is why martial arts was shrouded in mystery. If the guy knew your secret technique the chances of it working were greatly reduced...
So much of the traditional 'Old School' stuff does indeed look very martial artsy but we shouldn't throw the baby out with the bathwater. Give these principles some respect and some consideration and you will see they are universally applicable even when the context changes. So ignore the white suit and the rising block and see how and when you could adapt this great take down to suit your self defence needs...