Alas I have no insight on the statistics of who wants what.
I think it's a tough call for them. I too would prefer a sequel to Rebellion, but as I posted here many times I think that will be hard to pull off. They set the bar really really high with Rebellion and it won't be easy to make a sequel that will be on the same level. If they pulled it off it would be amazing, but it seems like it could very easily fail to live up to expectations.
This is a safer bet. It's easier to do a side-story, and if it bombs then it won't really impact the extant storyline.
I'm looking forward to seeing it but my expectations are that it will be a fun side story and not as serious as the TV/Rebellion.