Remember, this is in York Region. Any suburban area within 10 km of an historic village is considered within said village...
IMO, it's debatable whether old Thornhill even qualifies as an historic village as it has no streetwall or on-street parking. There's some old buildings along Yonge, but nothing really resembling an actual village. Looks like an older suburban area basically.
There are literally buildings dating to the early 1800s, less than a block from Yonge.
The early 1800s!
There are buildings right on Yonge from before the Civil War! Painters from the Group of 7 lived in the area.
I mean... what more do you want? Are there buildings even half that old in Thorncliffe Park?
What do you have to do to qualify? Have on-street parking???
Here, take a walk around..
There's a whole sub-debate here about heritage but I'll simply say this, based on your criteria: you seem to think "Heritage Village" = Unionville or Niagara-on-the-Lake. Unionville (Newmarket is another good example) have preserved cores largely because they are off the main artery. Thornhill is right on Yonge and so is Richmond Hill, which is slightly better preserved, in terms of the streetwall. So, unquestionably heritage has been lost over the years. But the idea that it's not enough to justify preservation is mind-blowing (but very TORONTO!) to me.
So, Immagonnasay that having dozens of houses from the early 19th century on either side of Yonge is a far better gauge of heritage significance than, um, on-street parking. Pretty sure the Ontario Heritage Act backs me up on this and that's more important than what any given individual thinks is "special."
Any-who, Markham Council has now explicitly passed a motion against the Option 3 alignment. Vaughan may have too; or maybe it's on their agenda? Either way, it's an uprising. (And, to the original point, aside from 3 or 4 buildings on Yonge, nothing in the Royal Orchard area - the area the tunnel would go under - has any heritage significance. That area is just a subdivision, but there are a couple of old houses (now housing businesses) directly on Yonge. but they'd be fine so...shrug.)
[EDIT - just to add I'm still facepalming over the idea that a heritage area is defined by "on-street parking." WHAT DOES THAT EVEN MEAN?
Does that mean Yonge and Lawrence is a Heritage Village?? Yikes,]