Itanium was not "an adoption" of PA-RISC. It was a completely novel design co-developed with HP after HP researchers argued that VLIW was the next step forward.
It did, however, manage to kill several of Intel's potential high end competitors with nothing more than hype.
at least $10 Billions of dollars (still bleeding, though at a much lower rate these days), some goodwill from customers, and letting AMD become the premier 64-bit platform from a couple of years and having to play catchup -- Intel was practically forced to adopt the AMD64 architecture or they would have lost the lucrative market for PCs and servers.
All things considered, I'm not sure that the price Intel paid for killing PA-RISC was good value for money - it was a lot more than hype, even if in the grand scheme of things it wasn't much.
Oh, it was a bad idea from the get-go. That was the sentiment I had myself, and heard from everyone who had actually looked at the details -- long before actual hardware was available.
The market did NOT want Itanium, and Intel knew that - but intel believed that they were strong enough to dictate. They weren't, and their internal culture made it hard for them to accept that for a long time.
I actually find it fascinating - Intel had an OO processor (name escapes me now) between the 286 and the 386 that has a story surprisingly similar to the Itanium: Radical departure towards unproven instruction set which, when arrived, delivered too-little-too-late, causing the company to scramble into retrofitting the older cash-cow for the future before someone else manages to eat their lunch.
It was iAPX 432. IIRC, its main problem was that it was ahead of its time. It was complex, and the manufacturing process was not developed enough, so it had to be manufactured as three separate chips. This made motherboards more complex, and also performance suffered.
I don't think "ahead of its time" is a good description (or, alternatively, it was so far ahead that its time had not yet arrived).
There was one CPU architecture designed since, that I'm aware of, that has OO baked in as well as a stack-machine model (the defining features of the software side of the 432, even if the hardware was perfect). The Java CPUs faired about as well as the 432, which is "not well at all". I think "bad architecture" is a better description than "ahead of its time", which is just as true for the Itanium.
The Pentium Pro seriously maimed Alpha and MIPS, but they still limped along bleeding profusely. Itanium is what delivered the killing blow, but I agree that even without Itanium MIPS and Alpha would have died soon enough.
It did, however, manage to kill several of Intel's potential high end competitors with nothing more than hype.