Is this comment on Reddit wishful thinking or something likely?
The House can compel Barr to submit the non-redacted version. If he refuses to comply, the House can hold vote for a contempt of congress charge against Barr. If that vote passes, at the House's discretion, Barr can be held by the House Sergeant-at-Arms for up to a year or until the House's demand has been satisfied. And if Trump were to issue a pardon for Barr for the contempt charge, Congress may choose to ignore it as the charge against Barr would not have originated in the judicial system and would be outside the authority of the President to intervene. The best part - SCOTUS has repeatedly affirmed Congress' authority to do this in the past on the grounds that the judiciary has no authority to rule over the operations of the legislature due to separation of powers. Even if the current SCOTUS would accept to hear a case resulting from this circumstance Barr would still have to sit in jail due to prior precedent until SCOTUS can hear and rule on the case, which could still take months to do.
If Barr wants to hide the President's secrets, let him do so from a jail cell.