Actually there is very little office space remaining in Hullmark ... those signs mean nothing, they never take em down.
Having said that that doesn't mean demand for office space is high, keep in mind the office space was sold as "condo" offices, implying many very small tenants, picture layers / medical / very small business.
Anyway, one can't describe the office market in NYCC week ... that's very inaccurate, the vacancy rates in the area are very low (at time over the last decade lower then downtown) and roughly the second lowest in the GTA (or thrid if you count the Bloor Market as separate ... which you should its just about as large).
The office market in NYCC is week for developers, not tenants; Essentially, to justify the cost of building, which isn't much less then downtown, and given Toronto's very high commercial tax rate compared to the 905, developers (i.e. the landlords) can't charge rents high enough to justify the costs ... that's why you don't see any construction, its not demand ...
Downtown can get away with it as firms are willing to make more in the way of rents.
NYCC does compete more directly with the 905 (i.e. along Hi-way 7 namely), I think VCC (not so much downtown Markham) will likely soften the NYCC market as it'll very much be direct competition. That is firms that want a somewhat urban setting, with subway access.
We already know KMPG is likely relocating all their offices around Yonge and York Mills to VCC.
There were rumors floating back of a new office building on the site next to Emarld Park. I can see it happening, but that's it, there won't be much office development in NYCC unless Toronto doesn't something about the tax rate differential, which it is, but extremely slowly, the absolute commercial tax rates are still roughly 1.7-2X higher then anywhere in the 905.