Thank you.
I don't think the appointment of bilingual judges to the Supreme Court of Canada affects one of its essential features. I am actually sure it does not.
As long as an essential feature is not affected, Parliament may amend the Supreme Court Act. I repeat: as long as an essential feature is not affected.
In the case at hand, bilingualism could be imposed through an amendment to the Supreme Court Act. If the Government of Canada has any fears that it is illegal, it can always refer the matter to the Supreme Court and ask the question head on. However, this can also be done through an amendment to the Official Languages Act, in which case section 16 of the act would apply to the Supreme Court judges as well as to other judges of the federal courts. This can also be done by passing a new piece of legislation, albeit a scenario that seems less likely, but nevertheless theoretically possible. This would be done by passing new legislation that would provide for the appointment of bilingual judges to the Supreme Court of Canada.
The question is figuring out what we mean by “bilingual” judges.