That was the point. To enable true downsizing, variable compression is the necessary technology. Turbocharged engines need to run at competitive compression ratios when off-boost and that will eliminate the biggest obstacle to the full benefit of downsizing. Variable compression turbocharging could be proven uneconomical in the near future, and it's up to Nissan to show the 2.0 VC-T is financially sustainable.
As you just pointed out yourself, variable compression technology is quite expensive to implement. Furthermore, Toyota has done research on variable compression. Toyota does research on many, many things. If you dig deep and follow the news out of Japan, some concerns still exist about long-term reliability and durability of variable compression engines. I doubt Toyota will be implementing variable compression anytime soon.
Reliability and durability are paramount at Toyota. When you consider the fact that Toyota engineers for a long time have felt hydraulic VVT systems are not reliable enough, that shows you Toyota's dedication to reliability. So unless Toyota comes up with a unique spin on variable compression technology, they are unlikely to implement it anytime soon.
Another somewhat modern example is direct injection. Yes it has benefits, but direct injection also has drawbacks. Normal direct injection systems all eventually lead to clogged fuel systems and significant carbon build up inside the engine which is expensive to clean out. Some automakers have come up with poor workarounds for this. What did Toyota do? They came up with a unique (at the time, and still relatively unique) system more than 10 years ago combining port injection with direct injection. This solved the problems and drawbacks of normal direct injection systems.
Likewise, Toyota has researched HCCI for many years, but I don't see implementation anytime soon as significant hurdles remain. Even Mazda's upcoming SkyActive-X system is only a half-measure or partial implementation of HCCI. It is not a real, full system because even Mazda engineers came to the conclusion that currently too many real world hurdles remain to implement a full HCCI system.
Otherwise what do you think the V35A-FTS is
An exception. Again, what do you think the A25A and M20A are? You can continue to ignore the stark evidence I have presented, but it doesn't change the fact that there currently is zero concrete evidence or even indications that Toyota will implement a downsizing strategy in the near future.
Here's another fact; downsizing was debated internally at Toyota over the last few years. Specifically it applies to the XV70 Camry. Implementing a turbo 4 cylinder instead of a V6 as the top engine option was discussed and considered internally, but Toyota decided
against downsizing. Toyota looked at owner and customer feedback, and there was a strong dislike against the idea of a downsized turbo 4 cylinder, while at the same time a strong preference for the V6 engine. So Toyota kept the V6 in the Camry. Likewise the new Avalon and ES both keep the V6 as the top engine option.
Mind you hybridization is another way of downsizing. By that definition Toyota is already committed to downsizing. What I was saying was not self-contradictory.
If you doubt the validity of downsizing, read the research papers Levi posted above. They come straight out of Toyota's own research center
Calling hybridization downsizing is very debatable, and some mental gymnastics apply here.
Is the new Camry's hybrid system "downsized" compared to the A25A? Of course not, it's an upsize overall. Is the hybrid system "downsized" compared to the V6? Well yes and no. The hybrid system is not meant to compete directly with the V6. So in reality, the hybrid system is a middle powertrain option that's an upsize from the A25A, and a totally different option to the V6.
Or how about we look at the history of the Prius. Over the years and generations Toyota has
upsized, not downsized the Prius hybrid system.
Research is just that, research. Toyota researches many, many things that never make it to production.
If you insist I post proof of my argument, then I have to say you need to overcome a language barrier first. Most of my (advanced) automotive engineering knowledge come from a group of drivetrain engineers on zhihu.com who are generous enough to show parts of their work that are safe to post to the public domain. Unfortunately for you these sources are in Chinese, and those guys who wrote these posts do not allow repost of these information on a different site.
A particularly interesting person is head of drivetrain calibration at TMEC Suzhou who was in charge of calibration of the 6AR-FSE, 8NR-FTS, A25A-FXS, and A20A-FKS. I will try to get permission from this guy to post translations at a future date so stay tuned.
Just to be perfectly clear, I am approaching this discussion from a global point of view. Toyota is a global company after all. I don't know for sure if you are approaching this discussion strictly from your own local regional perspective, because if you are then it's quite pointless in my opinion.
What some engineers may say or think in the Chinese region does not necessarily apply to Toyota on a global basis. I am looking at all the evidence and documentation from Japan, as it pertains to Toyota on a global basis. Regional differences always exist, but what matters in this discussion is Toyota's ultimate global philosophy.
Here's another stark point. Over the last few years various Toyota executives have actually mentioned that they don't see much point in implementing a full, across-the-board downsizing strategy. A couple of Toyota execs flat out came out and said that Toyota would not be implementing such a thing. Again, engines like the V35A or the (not a Dynamic Force engine) 8AR are exceptions.
Maybe in the far-off future Toyota may actually move to downsizing upon bringing to production unique versions of revolutionary technology like variable compression or HCCI. As it pertains to this discussion though, I talk about the future in terms of the short and mid-term future.
I'll end this post with this thought. Decades ago in the 1960s Wankel engines were talked about as a revolutionary new technology to downsize engines. There was a lot of excitement and discussion when Mazda brought out a production Wankel engine. So after all these decades did the Wankel engine take the auto industry by storm? Definitely not. In reality all the advantages on paper didn't amount to much. In reality significant problems appeared with the engine design in real world usage. Since then, only Mazda remains as the sole company still clinging to Wankel engines. What is my point here? Just because certain ideas or technologies seem revolutionary on paper, does not always mean they end up revolutionary in real world usage.