I know only few people who maintained software for Itanium, but from their reports it was a nightmare to debug code on. To have a chance to see what was going on, you would have to use special debug builds that disabled all explicit parallelism. Debugging optimized code was almost impossible, and user-provided crash dumps were similarly useless. Your only hope would be that the issue was reproducible in debug builds or on other architectures.
Needless to say, they hated it and were happy when ia64 was finally phased out.
> once the computing world finally moves on from C.
Yeah, it moves on from C... to JavaScript. Making compilers slow and complex doesn't mix well with JIT compilation.
One thing I have to give Itanium credit for is that due to EPIC it was totally safe from the speculative execution vulnerabilities like Spectre/Meltdown/etc. That was certainly a forward-looking aspect of it.