Final answer:
The implication of datatype() only returning declared datatypes is that the programming environment employs strict type checking, preventing automatic type conversion and leading to type errors if types are mismatched.
Step-by-step explanation:
If the function datatype() only returns declared datatypes, this implies that there is a strict type checking system in place within the programming environment. Such a system would not allow for type coercion, where variables and values convert automatically to another datatype without explicit conversion.
In programming languages like Python, Java, or C++, data types define the type of data a variable can hold, such as integers, floats, or strings. If datatype() only identifies declared types, then variables must be cast to the correct type before operations can be performed, and type errors are likely to be thrown if mismatched types are used.