Starrmark wrote: However, I am not suggesting that donations to IMSLP should necessarily be tax-deductible. Since IMSLP is based in Canada, and most of its users are in countries spread over the world, tax-deductibility would not be of much of an inducement to make donations. I think it will not make much difference to IMSLP's bottom line if it goes non-profit.
Except it isn't based in Canada, it's registered as an LLC in the US. It doesn't have a legal identity in Canada.
The point of it becoming a non-profit organization is not (only) to make contributions tax-deductible, it's to ensure IMSLP is not controlled by and dependant on the will of a single person, and to make the administrators accountable to the members (as well as, obviously, prevent that the monetization of the service could generate profits for the administrator(s) )