If players start using other techniques besides leg take-downs then it is a successful albeit extreme solution.
The question is why they want players to refrain from using leg take-downs.
It could be because of influence from purists. If this rule is something that only the USJA is doing then maybe it is not about "pure judo". Maybe they feel too many US players are relying on their wrestling too much. So much so that is a crutch instead of an advantage.
If we consider the dearth of Olympic and World Championship success of US players then maybe the USJA believes eliminating attacks below the belt will force players to train techniques they are not good at instead of take-downs they may already be good at. They could make the point that players are winning at the local and national level with their wrestling reinforcing training of take-downs. But which leaves them vulnerable at the international level.
I don't know that this is the case, I am just throwing some ideas out there.
In regards to the purists, I have read debate about this in Japan. The debate does not concern which techniques are pure. The debate was about whether players were winning by ippon. There are the traditionalists in Japan who believe pure judo or Japanese judo is winning by ippon. There are some non-traditionalists who think that maybe this mindset should change and that we should accept winning by points or at least not throw out the possibility of winning on points.
Reading some of the traditionalists arguments could be summed up in three rules.
You must win by ippon
Losing is better than winning by points
3 Losing is unacceptable
Before the Beijing Olympics, Satoshi Ishii was heavily criticized for his propensity to win by points. I was surprised some sports publications were ignoring his chances of medaling at the Olympics. I think the traditionalists view of Judo influenced the media's view of him.
Ishii eventually won gold, and his performance was "acceptable". Ishii finally was doing real judo some pundits would say.
Maybe take-downs no matter how good you are at them are not enough to have sustained success(as a program) in Judo at the international level. Maybe the USJA thinks this and this is what they are doing to fix the problem.
I do not think simply take-downs are the source if US judo's lack of international success, it is a much more complex problem. But if one was to look at the sustained success of the Japanese players, like an Inoue who wins multiple world championships and Olympic gold, probably undersized for his division, with uchi mata. Or Koga's success with seionage. Maybe there are some US officials thinking "Why can't we do that?â??. And I am sure that the US could develop players like that.