For blockchain consensus you need 100% precise behaviour and even languages like C++ are problematic when it comes to that (if Bitcoin were to be compiled with say VC++ you might find some unusual compiler bug/quirk that means it won't agree with the g++ builds).
just thinking:
if there will be a meta language described in the RFC which can be used to check a block/transaction by hand this may be enough.
If we encounter on a compiler/compiled version to check something this will be hard in the future.
a clear definition will be better. Sure, there can be problems when an implementation will not be precise enough or a compiler will make something wrong. But the same can happen if you have buggy hardware (memory errors for example)..
but, this is just a loud thinking if it will possible to go away from the g++ builds to a more abstract layer