Indentured servitude requires someone to work for a particular employer for a fixed period of time. ISAs do not do this.

Words have meanings. You don't get to just ignore them to make an emotional point.

Excepting that they aren't able to 'sell' your labor to a third party, nor are you expected to work for them after graduation.

Not quite. You can find it if you're looking for it, but I've known and heard of some companies helping out with student payment programs or scholarships under the pretense that you will work for them at an agreed upon salary, albeit a bit lower than standard.

The initial case in the article suggests something similar where investors will "invest" in a student and bank on a successful career with repayments, similar to a student loan. I can't see this as being a negative that Indentured Servitude was.

The notion that paying back a loan based on percentage of money earned is indentured servitude seems to skirt very close to the libertarian memes that taxation is theft/indentured servitude.