There's one caveat: advanced branch prediction is probably not free. It probably costs a bit of silicon, even some energy. It may or may not actually matter (I'm no hardware designer), but if it does, we may have to make some hard choices, like a few more cores vs badass branch prediction.

It may not matter on X86 specifically, where out of order stuff dominates anyway. But it might matter for stuff like the Mill CPU architecture, for which energy efficiency and not wasting silicon is very important.

> advanced branch prediction is probably not free

I wouldn't be surprised that in this particular case it's even more about the patents and the possibility to have an advantage to the competition than the silicon. Anybody knows if there is a patent? If there is, who holds it? How much would the CPU which would implement that method cost more?

If someone identifies an optimum (for performance, efficiency), all competitors are forced to go there to stay competitive. We already have more cores then we know what to do with, and better single core performance is always appreciated, so badass branch prediction probably wins out IF they find that it is useful at all (these days, meaningful gains on single core are difficult to eke out).

> say today X does no good on brand new hardware

Is for you the "brand new hardware" your desktop which spends hundred of watts per hour or your mobile phone which has to survive the whole day without recharging his 5 Wh battery but still let you surf the web with all the stuff you take as given? Making optimizations that work good with lower wattage CPUs is a good thing, unless you limit yourself only to the non-battery devices.

Mobile architectures are typically only a tock away from desktop architectures, who aren't really guzzling energy with these optimizations (the deep pentium 4 pipelines are behind us!). So if technology marches forward, there isn't some mobile version that is frozen in time just because of energy efficiency (indeed, good branch prediction saves energy also). There are no 386 or 486 CPUs to care about now, while P5s are limited to that Phi HPC product.