Any chance Richmond Hill line is going to get extended north? Since the Stouffville line is pretty much a dead end, and can't be extended.
The Stouffville line is not a dead end; the track does in fact go further; to Uxbridge; though beyond Lincolnville the track is not in GO-train worthy condition, as I recall.
The track could be extended beyond Uxbridge, as the Right-of-Way is largely in tact, but for a couple bits in Lindsay.
That said, its been discussed here often that there probably isn't much merit to extending the line at this time, as the area in question is quite rural and low-density, and most of us wouldn't want that to change.
The Bala sub (Richmond Hill) line is the CN mainline and as such goes on for a vast distance; but beyond the future Bloomington Station it also doesn't serve much as it gets further north, from a commuter point of view. I suppose one could go as far as Aurora Road; but Aurora already has service, so I don't see much value there.
I don't really want to see density on the east side of Lake Simcoe.
The extension of lines, at least for commuter rail purposes, should, to my mind, be tied to the existing commuter-shed; and/or serving a population centre of significance.
In that vein, further extensions of LSE and LSW to Bomanville and Hamilton++ are already in the near-term offing.
I would expect, that service to Cambridge would rank next on the list; likely via the K-W corridor; though possibly via the Milton corridor as well. Though a preliminary study favoured the former.