I disagree, I think its likely Sheppard will be extended, to the west, in particular.
There is a need to be able to bring trains from Wilson Yard to the east side of the line in a more timely way.
This would make it easier to start service earlier/run it later as well; right now a lot of time gets soaked up by run time from Finch (soon to be #7) all the way back to Wilson.
While the Northern extension will likely have some train storage; its unlikely to have heavy maintenance, or sufficient capacity to resolve the the scheduling issue.
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In addition to that, the TTC is openly considering extending the existing Sheppard Line stations to handle 6-car trains; that's an unlikely investment to make if one was considering converting the line to an alternate technology.
I'm not persuaded there's any case to be made in the near/medium term for Sheppard extending eastward beyond VP; nor do I think that extension is any way imminent.
Still, the notion that Sheppard will be converted isn't supported by the evidence of which I am aware.
I also think the western extension is likely, in the medium term.