I don't think he was specifically talking about Serena, I want this as much as you do, but I think the animator was saying to watch the ending of XYZ as whole finish and I agree with Zelda, everyone want you to watch what you made, dosent mean you'll get what you want in the end of it. Still, it could happen, but like I said 99% sure that Serena leaves, but she will get a great conclusion.
In respond to DatsRight, it's Omode's last XYZ writing, not the final. At least I think so, in the tweet Omode said that it would be the last one that would be written.
Here's what translate says: " My XY & Z screenplay responsible times also, one story rest. It is lonely. " And yes, it will have a bitter taste, but if AmourShipping gets the conclusion we want then the salt would be stemmed.
Read what Ashserena said above, she is Japanese and she translated it better than google