By offering prices in the same ballpark (<50% higher) with other top unis (UBC/UofT), McGill was a good choice for high caliber students across Canada. This means, for QC students, an opportunity to study with the brightest across Canada, rather than having to move to a different province.
Now, a lot of top Canadian students will choose other options as they would be $36k+ less than what they would have paid at other top unis. Long term, this will hurt the reputation of McGill, as it will become the school of "my parents paid for my tuition fees" and "I had to take a 75k loan because I couldn't get into UBC/UofT".
This could, potentially, result in more francophone students choosing to leave Montreal to study at a school with top students coming from all over Canada.