Let's look at it through this lens. What percentage of revenue the NCAA brings in (TV, sponsorships, etc.) should go to the student athletes? 51% like the NBA (or NFL, I forget). 80%? 20%? Then see how much the NCAA brings in, divided by the number of scholarship athletes, and bam, you have a number. It doesn't have to be hard.
What percentage does the school receive? One might argue that the $$ received the school receives (assuming that it is directed largely toward classrooms/facilities, faculty recruitment and retention,student services) provides support for ALL the students, including student athletes. Having the money go to the university athletic department results in outrageous salaries for assistant coaches and other scandalous expenditures like lazy rivers next to the athletic dorms (I think I saw that the strength coach at Alabama makes more than the University president).
The article in the twitter link points out that 98% of student athletes go on to non-professional sports occupations. Spreading the money around to benefit all students seems reasonably equitable.