“So far” means to this point in time. For example, “So far, no one has been able to reach the top of the volcano”. “By now” is used to express the expectation that something should have happened by this point in time. “John is very late and should be home from work by now”.

‘By now he will be in Oxford’ means that he has reached his destination, he may go further or he may stop there. ‘So far he has got to Oxford’ means that he has got to Oxford, but he will also carry on. The phrase means that he hasn’t finished his journey. Is this the context you meant? 