I’m not sure Itanium was a technical failure, to me it always was a business model failure as that CPU was co-developed with HP and essentially became a dedicated HP-Oracle box and by the time the ecosystem was opened up it was too late.
The heavy reliance on the compiler for ILP was an “odd-choice” but not something that was unsound in principle.
If the ecosystem was more open from the get go and more vendors were involved it had a much better chance of taking off.
And if nothing else at least it was something new.
The biggest disappointment I have with Itanium is that it and later Larabee/XeonPhi kinda pushed Intel even further into their own little x86 box when it came to processing units.
I think that failure is also why they haven’t really done anything interesting with Altera.