By definition and practicality, schools and fields of work will remain a pyramid i.e. at any given time, there will only be a few fields and colleges that "give advantage", being able to absorb only a fraction of students by competition. e.g. field of programming can only absorb a million odd engineers in next few years. (Ironically, when it absorbs more, it will no longer remain a field with high wages).
The remainder of the iceberg hence, will need to go to other lower parts of the pyramid. ISAs won't do anything for that. Only the government will. And the Govt does it for us, with our money, because not providing education to lower levels of pyramid will result in nothing but societal anarchy.
ISAs hence shouldn't be hailed as panacea for education loans which is what marketing makes us believe. The only advantage of ISAs, is that they unlock better education for some "motivated students" (for lack of an accurate phrase) from underprivileged circumstances. That's not a trivial advantage for those who qualify. I don't know what that % of population is, but it can't be much.
In any case, however small, that number sure seems enough to build a business around it with some feel-good marketing (like this article).