The BBC were happy with the ratings from the show and the only thing holding it back is Richard Curtis getting around to organizing a 2nd Season. So fans should expect another 6 episodes within the next 2 years. The decision hasn’t been made by Curtis to go forward yet, but I’m sure it will happen. He’ll want to keep the quality as high as it was, so just give them time.
HBO will pick it up if it exists. The only other delay I see is the recent restructuring of The Weinstein Company. It took them years to get the first season going so don’t take any delay to mean it won’t be back.