It's enough to meet McGuinty's hourly service promise; 6-km between York U and Rutherford. Just enough that 2 trains can pass each-other running in opposite directions.
The EA to double track (triple track some sections?) nearly the entire corridor (for RER) is expected to be finished in December 2016 (start "early" 2016) though I cannot find anything to indicate it's currently in progress. The small chunk with the Davenport grade separation is a separate EA from the rest of the corridor.
Hourly service, but only as far as Maple or King City, given that it takes 25 minutes from Rutherford to Aurora and 52 minutes from Union to Aurora. Hourly service any further north would require another siding to allow 3 trainsets on the line.
With luck, they'll be able to start tendering bridge rebuilds as this small piece of double-tracking is finished.
Bridge rebuilds for widening? South of Aurora, all the bridges already support at least two tracks:
Dundas: 2 tracks (overpass)
Bloor: 2 tracks
Dupont: 3 tracks
Davenport: 3 tracks
St. Clair: 2 tracks
Rogers: 2 tracks
Eglinton: 2 tracks (overpass)
Lawrence: 3 tracks
Wilson: 3 tracks
Hwy 401: 3 tracks (?)(overpass)
Sheppard: 3 tracks - some plans for Downsview Park station depict 3 tracks with 2 side platforms
Finch: 3 tracks
Steeles: 2 tracks
CN York Sub: 2 tracks
Hwy 407: 2 tracks
Hwy 7: 2 tracks
Don River: 3 tracks (double tracking under construction)
Major Mac: 2 tracks
Keele: 2 tracks (overpass; already double-tracked)
King Rd/Keele: 2 tracks (overpass)
Bathurst: 2 tracks (overpass)
It looks like the line was double-tracked at some point in the past, which makes me wonder why we even need an EA for the southern portion of the line.
In and north of Aurora, there are some single-tracked bridges, but there are also enough other constraints that I assume those bridge rebuilds will come about from the general study on double tracking.