I think this should not be done. Note that even though code which is D could reintroduce commas safely, C code will still exist at that time, and likely need porting to D. The principle that C code should either do the same thing, or not compile, would be violated.
What would be an example of C code that would compile in a D where the comma operator was used for tuples? Also why is cut and pasting C code to D so important? If it's non-trivial surely people will just use extern C. If it's trivial they can make the minor improvements necessary.
