What if Flynn really still is a Trump loyalist? By copping a plea to lying, he is seriously compromising his usefulness as a witness, and a source. It's called the doctrine of, "The Fruit of the Poisoned Tree",
Fruit of the Poisoned Tree
If Flynn is really a Trump loyalist he could nullify his usefulness to the Mueller investigation by copping to perjury. Remember the O.J. Simpson murder trial? Mark Furhman, the lead investigator, perjured himself on the stand, (and was convicted of perjury for it), under "The Fruit of the Poisoned Tree" doctrine every piece of evidence that passed through his hands was stricken from the record! 90% of the case against O.J. went down the drain and O.J. walked.
By copping to lying Flynn is only a very small step away from the above move. Flynn is now an admitted liar. How is Mueller going to get anything he says to be reliable. How does anyone believe anything he says? Yes it is still admissible. But, dang, if you were a prosecutor would you actually put him on the stand? Would you try to USE anything he leads you to? The jury might just die laughing!