If maxima talks to a frontend like wxMaxima it no more seems to be able to tell at which position the error was. Counting the lines of the input file doesn't make sense in this case, since there is no such file. But telling which char in the current command the error is found at would allow the frontend to place the cursor there.
Can you give an example of how that would work? I think there is some attempt in the input parser to identify the line and character position when there's a syntax error; maybe that can be adjusted to be more helpful to a UI. An example would help clear it up.