I only wish that the performance focus was there back in .NET 1.0, with the main architect coming from Delphi, but Microsoft had other priorities.
Also can we please have proper syntax for inline arrays instead of a special purpose attribute? Don't really get that one.
While I kinda agree (And IMO ask whether having proper syntax would be a stepping stone to other things in future like proper alignment for 16-byte fields so we could sanely do cmpxchg16b), if I had to guess, it's because there's other existing code to handle StructLayoutAttribute, so just doing another attribute versus having a field probably was the 'easiest' way to implement across the different bits of the JIT and GC.
The excuse of breaking existing code doesn't even work, as there are other keywords that are context specific, and for those there was no problem introducing them.