This should be core functionality on QBO - it is the only way to have an audit trail of the entries being recorded. An audit will have a horrible time auditing QBO general ledger and picking transactions for testing as they can not easily see the other side of the transaction in the GL. 

Very relieved i am still on desktop - i only discovered this as i was helping someone using QBO and said - show tranID - and was shocked to learn this is NOT possible. Not sure why it is not given it MUST exist.