Metrolinx is very fuzzy with the details on the rollout. The intial rollout of presto coincides with the rollout of the new streetcars. At he moment, The end of 2015 is all I can tell you for all streetcars.
New PRESTO readers for the UP Express.
From the torontonist: http://torontoist.com/2015/03/riding-the-union-pearson-express/slide/20150309-torontoist-up-201/