Well, realistically, I would wish for more Charming family bonding scenes with Emma/Charming and Emma/Snow and all three of them together. I would also wish for another Emma flashback to the real world.
But since this is to wish for anything, I will list things I want to see that will never happen.
An episode devoted entirely to what the fairies are doing at the Convent, including a flashback showing what preparations Blue was making before the Curse, and another flashback to show how she became the Blue Fairy in the first place many eons ago. And then having her be useful on a regular basis as a sage and an advisor and as a teacher of magic to Emma.
An episode showing Granny's childhood and how she gained her awesome combat skills. Maybe she crossed realms as a child by accident and ended up as a Joan of Arc type figure. And then another flashback showing how Granny came to adopt Red.
An episode showing Cinderella's life before the Fairy Godmother, with a special guest appearance by Anastasia from the Wonderland show, and also revealing where Thomas disappeared to after Cinders tricked Rumple into signing the scroll.
An episode showing how Maleficient put Aurora Sr. into deep sleep, and how all that turned out, and also how Aurora Jr. got into her deep sleep and how she met Philip
Another spinoff idea is to just tell stand-alone "untold" stories for 10-13 episodes about the backstories of all the minor (and usually ignored) supporting characters like Grumpy, Archie, Geppetto, Granny, Blue, plus all the guest starring characters who never got a flashback (eg. Mulan) or those characters who reached a happy ending but we never saw much of it (eg. Frederick & Abigail, Eric & Ariel, Hansel & Gretel, etc.)
Unfortunately, without a continuing story, that might not get people to tune in... but there is so much untapped potential with all the minor characters. I know the focus of the main show needs to be on the main protagonists, who themselves are often ignored (eg. Charming), but I see all those people standing in the background as glorified extras and I want to see more of them.