My apologies on this update taking so long to post, I was in San Diego all weekend and couldn't get to a computer with enough time to post it. Now that I have returned home, I am now getting to it.

We're at the halfway mark now, folks! Week 26 out of 52!!!
So far, the Xbox One and Nintendo Switch are up YoY, while the PS4 is down.

I decided to do some calculations and found the percentages of what all three systems were at this point last year, compared to what they finished the year with.
For PS4, by week 26, it had sold through ~39% of what its 2017 totals were.
For Xbox One, it had sold through ~27% of its 2017 totals.
For Nintendo Switch, ~32%.

If those same exact percentages were to hold for this year, this would be the 2018 totals for all three systems:
PS4: 17,949,895
XBO: 8,933,393
NS: 16,273,149

Now, this is just a rough hypothesis. A ballpark estimate if you will. Out of the three, I believe the Nintendo Switch's estimate is likely to be the most accurate since we know, more or less, what Nintendo's lineup is for the rest of the year and they usually don't do anything special, in terms of deals, bundles, or price cuts, for the holiday season.
On the other hand, the PS4 and Xbox One will be trickier to predict. The PS4 should continue to fall further behind 2017, especially in the coming weeks with Dragon Quest XI's launch doing huge numbers in Japan. It will basically keep going down until the week when Spider-Man launches, where 2018 should win that week, afterwards, there's FIFA 19, Battlefield V, Black Ops IIII, RDR2, all of which should have some big effects in October. The real question mark will be what Sony has planned for November and December. Will they do another big deal similar to the $199 Black Friday PS4 deal they did last year, as well as the $349 PS4 Pro and $249 Star Wars bundle during December? That would be a big factor for how much it sells for the rest of the year.

The Xbox One should continue on soaring up through the atmosphere (Mary Poppins reference, anyone?) until.... the launch of the Xbox One X. The biggest reason... really the only reason why the Xbox One has the lowest percentage of the three listed is because of the X model. Once that system's launch week kicks in, all hell will break loose and we will have to see what will Microsoft's plans be to hold off that launch and remain up YoY.

The trend continues. I think Switch will be flat or slightly down next quarter tho. And then it will explode again on the last quarter of the year, but more than last year. All in all, I'm expecting 17m sold this year, so almost like your estimates (16.3m).

We shall see. The next 3 weeks will be important. The first two will be the same story as always, but then the 3rd is when Splatoon 2 released, and from that point on was when stock began to catch up. So both years should be on a much more level playing field. That said, I expect this year to be slightly up YoY.

Well the baseline went from 120k to 160k, with some dips here and there. I don't think the Switch will dip that low

Honestly it probably already dropped to that level. I dont agree with Quickrick on many things but i do think hes right that Switch has been overtracked quite a bit in Europe/RotW each week.

But not to the degree he's proposing. He's saying that the Switch is overtracked by a Million, which would mean overtracked by about 70k per week. That would mean almost everything that's not Japan or US sales, and that can't be true. I do agree that it might be overtacked, just not by anything near that amount.

Speaking of overtracked: Considering european videogame sales charts the last couple weeks, I do think that the PS4 is even more overtracked there. Switch was keeping up well through April and May, and started seriously trashing PS4 game sales in June. So unless Switch has a gynormous attach rate or PS4 haz no gamez, PS4 is overtracked there as well.

Ya i dont agree on the amount either.

I'm wondering how is Octopath Traveller going to affect the Switch's sales. I doubt it will have any major effect in the west, but it could move a decent amount of units in Japan.

In Japan, I would expect it to be back above 50k at least.

Well, it looks like I guessed right.