Just saw this across various fineprint pages on the Spark Website. First I'd heard, certainly haven't had any emails or anything.
From March 1 2016 the option to reduce your broadband speed will be removed and Spark's data cap overage pricing will change and be charged at $5 per 5GB block of extra data, up to a maximum of $50 when we will put you on unlimited for the rest of the month.
I guess it is good from an industry / tech perspective. Will just have to be a little more careful with usage.