^For what it’s worth, the math backward plugging is still a suggested technique, by both Princeton Review and by Khan, e.g. https://www.khanacademy.org/test-prep/sat/new-sat-tips-planning/modal/v/effective-strategies-for-each-sat-section-9282016
Does this Khan practice-effect essentially render practice a requirement for many students to score at their highest potential compared to other students? I suppose it depends on how prevalent practice is. It seems as though the advertising of Khan by Coleman and the College Board could potentially make prep more widespread - it would be interesting to see data on proportions of kids in various score ranges who prep (with Khan or anything else) and whether that has changed in recent years.