I do not interpret the letter as Barr’s having any intention of releasing grand jury material.
His delay right now is simply to get it all identified so it can be redacted as required by law.
There will be two sets of things at issue here:
1) personal things involving Trump officials, etc., that should be redacted - people like Michael Cavuto. Redact OK
2) things that reveal - by their content or act - the coup things that are underlying everything. Investigations of these people that were fed via HRC + FusionGPS & F_I “Crossfire Hurricane” to the Trump campaign. Those things we want prosecuted and, then, after such underlying things are exposed (from the outside / other side), then those can be revealed :)