I can see them doing what TFL does in London wherein they have a daily cap. In London if you travel within Zones 1-2 for example your daily fare cap is 6.80 and nothing more. Their 7 day pass however costs less than 7 total days of the daily cap.
This would eliminate the need for a day pass and before anyone says.. oh but they still need a physical pass for tourists, the homeless or the convalescent allow me to say that is not an excuse. Honestly, very few cities have a group pass anymore. Most cities that have fare cards like Oyster eliminated the group passes in favour of a daily cap. The simple reason is that it is both impractical and impossible to have 2 or more people using the same card. While you MIGHT be able to program Presto to display it as a group pass to fare inspectors, it will still present problems at the gates in terms of anti-passback measures and the limited time to pass through the gates.
Cities like London and Paris have done away with paper or single use fare media in favour of fare cards. You can no longer buy tickets, passes or tokens in London. You can put money on a card but not buy tickets, tokens or pay cash. They do not have single use media like a day pass and the world has not come to an end.
All I am saying is in the next couple of years single use fare media will disappear in Toronto.