^^I could be wrong, but I don't believe any of those engines satisfy emissions regulations - not to mention Toyota would probably be panned by the press for releasing a new car with massive hype and an old engine, even though they'd be great to see in the 86 with modern tech.
Sadly, gone are the days when a company could hold onto an engine for decades, continually getting more and more out of it. I've got a mini with a BMC A series motor in it that was originally designed in the 40's-50's - people are still getting more and more out of them today (70 hp ATW in my car, but proven to get more than double that in a fully built engine... from a NA 1.3L 4 cylinder carby engine with only 3 exhaust ports).
Having said that, not all emissions technology is bad - Direct Injection has a lot of pro's as well, and from reading reviews seems to have given the boxer engine at least a bit of excitement potential (as long as the revs are kept up). Fiat's multiair tech will inevitably be reverse-engineered/licensed by other manufacturers too, and seems to be giving big power gains across the rev range along with better fuel economy (although not at the same time). Still, I'd love to have seen the 86 released with a small, Direct Injection, high revving straight six of Toyota's (and Yamahas) own design.
For me, a truly great car would be a small RWD fastback hatch (similar to the original AE86 in style, kerb weight under a tonne) with a lightweight, stratospheric revving 1.6L 4 cylinder, and all the latest whiz-bang jiggery to get the most out of the tiny engine. I'll have to keep dreaming though :)