Under the pending Trump Tax Plan, Universities whose endowments are above $500,000 per student will face an endowment income tax of 1% a year. A $7 billion dollar school would pay roughly $10 million dollars in cash (that's a lot of Assistant professors slots). Holding a university's endowment fixed, if this school increases its student population by 20%, it will be less likely to face this tax threshold. From the link above, I see that Duke, UPENN, Columbia and University of Chicago are all hovering around the threshold. I predict that they will be admitting more students in the near future.
My son is a junior in high school so this incentive effect is of interest to me.
UPDATE: This post has been updated to correct my mistake. The tax is on endowment income (not wealth). I thank USC Price Professor Nick Duquette for updating me.