The Highway 404 expansion between Major Mac and Stouffville Rd. appeared to be substantially complete when I drove through a few weeks ago. The expected completion is 2021, so I would say they are on target. The section between Major Mac and Hwy 407 still requires quite a bit of work. This section was a separate contract that includes the rehabilitation/replacement of the Rouge River, Beaver Creek and 16th Ave. overpasses and is not expected to be completed until 2022.
Yes, I've had the same opinion driving through it. Major Mack to Elgin Mills has been finished, including repaving all of the lanes and putting them back to full widths as opposed to narrow construction widths, since mid or late 2019 if memory serves (I used to commute that way). Elgin Mills to 19th Ave was pretty much finished earlier this year. I last drove the 404 about a month ago and they were very nearly done up to Stouffville, seemed like they had done some of the paving and were preparing to finish the rest. I think honestly they could easily enough open this stretch by the end of this year if they wanted to, though of course they won't with the Mack-407 stretch unfinished.
But yeah, the Major Mack to 407 stretch is not even close. I don't see it even being finished next year. They really ought to have started that stretch much earlier so that it could all open this year or early 2021, instead we'll have the HOV lane from the 401 to the 407, then a construction zone, then a fully finished HOV lane barricaded off from Major Mack to Stouffville, for a couple of years.
Goodness sake, though, they really need to get to work on widening the Aurora Rd-Green Lane stretch to 3 lanes. The northbound 404 at Aurora Road at most times of day has been a death trap for about a decade, with people swerving out of the right lane at the last minute--apparently there are so many people every hour of every day driving that stretch for the first time in their lives--and during/around PM rush hour the traffic regularly backs up almost to Bloomington. Even when I drive north from Aurora Road to Davis or Green Lane, or south through the same stretch, on weekdays around 11AM or 1PM while doing some shopping, the two lanes are just not sufficient for the traffic volume much of the time. It is common, at these off-peak times, to see a convoy of cars back to back close to each other in both lanes until you get out of that stretch.
Obviously eventually the same problem will appear at green lane, but in my experience right now the vast majority of the traffic is south of Green Lane. Another thing is that having the right lane exit is just a recipe for disaster, sooner or later...IMO they should have the right lane end maybe 1km after the exit, so that all of the merging for the off- and on-ramps has concluded, mixing all of that merging together in the same spot is awful. For now I don't think it would be a huge issue to have the new northbound right lane exit at Green Lane, but by 2030, it'll probably end up just as bad as Aurora Rd has been for the past decade.