Even though the original Open All Hours was a Ronnie Barker comedy vehicle, it worked because of the dynamic of the main relationship between him and David Jason. The shop as the main set needed two central characters and Granville was an ideal foil for Barker's Arkwright. To make the new series work, Granville will need someone to share the shop space with him and I have wondered whether this will mean the introduction of a totally new character or whether an existing character will have their roll expanded.
The other point to remember about the original series is that the relationship between Arkwright and Granville was to some degree age v youth. Granville was relatively young, mid 30's, early 40's and had largely missed out on his youth because of Arkwright. Granville fantasized a lot about the world and was a bit of a dreamer because he wanted something better, while Arkwright was a traditionalist, pragmatic and down to earth. Arkwright undoubtedly held Granville back, but only because he thought it was in his interest to do so,(which was also in Arkwright's interest of course).
The point is will a new younger character be introduced to recreate this relationship? Granville is now in his late 60's, early 70's, he has effectively become Arkwright, who's going to play off of him? If a new younger character is introduced I hope that they are not too young. It's not that I'm against that, it's just that I'm not convinced that Roy Clarke can write that role. If you look at LOTSW, his youngest character was Babs, a total disaster because she was so formulaic. Milburn was a better character, but even he was presented as somewhat backward.
The alternative is to have Granville Married or at least like Arkwright, promised to someone. The milk woman played by Barbara Flynn would be ideal, but she would now be working in the shop with him. Perhaps he has a son, a Granville junior? Hard to imagine, but it might work. He might even be named Damian!
What about Nurse Gladys? Would she still be a nurse, she must be in her 70's and one assumes retired by now? Did she finally marry Arkwright or did he pass on before they could wed? Whatever, chances are that Gladys is now a mother figure to Granville.
The thing is that Open All Hours ended in 1985, so it's getting on for 30 years, most of the original characters will now be much older. I do wonder if introducing younger characters will be welcomed by the older audience that remembers the original, but I'm not sure that it can work if it is just the older characters, especially if it is to become more than a one off. If it is to catch a wider family audience of all ages it may well need one or two younger characters.