Not to mention that the whole idea of the Mill requires a “sufficiently smart compiler”. We tried VLIW (based on the same compiler ideals) with the Itanium and it was a major flop.
The Itanium platform was totally unaffected by Spectre/Meltdown type attacks, you may note.
Intel didn't want to make 64-bit x86, but the market prefered amd64 over itanium.
Intel invested heavily into Itanium, and the 90s started seeing the deaths of competing processor architectures in part because of how hyped up the Intel Itanium was getting. It was intended to be the 64-bit version of x86, hence the abbreviation IA-64. AMD was the one who created what we now know as x86-64, and my understanding is that Microsoft more or less forced Intel to implement AMD's x86-64 specification.
In its later years (let's say by 2010, since that's the midpoint of Itanium's life as a shipping product, but I don't have any clear dates as to when the shift happens), it does seem to be that Intel was reluctant to continue supporting Itanium. But that was definitely not the case beforehand.
Ultimately, the compiler never materialized and I'm convinced they knew it wouldn't (but in the meantime, they almost killed all the RISC competition). The Halting problem means that at best you have heuristic optimizations that constantly fall through.
The only way to solve these problems with a high degree of success is to analyze the code as it is running which is what other CPUs actually do. This is so true that later versions of Itanium (latest being released in 2017) were just VLIW wrappers around a rather traditional, speculative core.
You are correct in as much that achieving this level of optimization through static analysis alone without cooperation in the language would be a very challenging problem. The folks at https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/ are taking a stab at it nonetheless - their approach requires language extensions.
I'd prefer not to ignore the issues of Spectre and Meltdown - doing so is what got us here in the first place. I still run many older machines in roles for which they are well suited and would gladly trade performance for more predictable and secure behavior.