A Madoka Magica project we need: a series showing in detail the first three timelines. To see why and how Homura became the desperate girl we met at the start of the series... And also to spread the answer to two questions: why did she take Mami's freak out so bad, and why did she believe two or three magical girls could take on Walpurgisnacht? Because, well, Madoka Magica Portable actually answers both questions in the Mami route.
If you play things right, get to a certain ending by grinding enough and fight dodging enough, you see MAMI. SOLO. WALPURGISNACHT. Yes, in the first timeline Mami took on Walpurgisnacht with Madoka and Homura watching on the sidelines and slowly shot it within an inch of its life, only for Walpurgisnacht to fire a last ditch attack at Madoka, attack that Mami took head on and died from. In the anime we then saw the immediate aftermath, Madoka going on and finishing off the monster at the cost of her life and Homura making her Contract.
And that is why Homura thought she could take on Walpurgisnacht with one or two other magical girls, SHE SAW IT HAPPEN. And why she took Mami's freak out so badly, that was the invincible mentor that almost solo'd a Witch closer to a hurricane than anything else.
And the hope in the viewers and its crushing would be amazing.
EDIT: I just realized that there's the fourth timeline too, as it both solves the mystery of how exactly Mami knew Walpurgisnacht was coming yet it's a surprise in the other timelines, and helps solidify Homura's change. Plus, it would give an anime to a certain spin off.
In the original timeline, Mami is warned by this new magical girl. She's timid, had a perfectly innocent reason for her wish, and has prophetic dreams - that's how she knew. She's also in the final battle, helping fend off Walpurgisnacht's familiars and taking extreme risks because she dreamed that if Mami dies they're all cooked, but she's knocked out protecting Homura and so can't take the hit for Mami. She wakes up after dreaming of Kriemlid Gretchen, and when she sees Homura transforming she tries to KILL HER - but is too late, and starts laughing mad.
In the second timeline she's initially the same as the first, but progressively becomes hostile to Homura specifically and more unhinged, and almost kills her - but tries to ally herself with Kyoko for the deed, and she instead warns her former friend.
In the third timeline she doesn't appear for a while, and when she does she's already unhinged, and begs everyone to keep Sayaka from contracting. And when Sayaka does, she suddenly attacks HITOMI out of nowhere, as Homura's time travel changed her powers and now she's a seer, and knows that if Hitomi gives her ultimatum it will result in Mami snapping, and she MUST survive to defeat Walpurgisnacht or they are all doomed. Sayaka saves Hitomi and wounds her, and she dies begging Sayaka to be strong, and tries to say something about Hitomi's intentions, but her Soul Gem cracks before she can finish.
Fourth timeline... Well, this magical girl is Oriko Mikuni, and if you know the name you know what happens here. And why in every new timeline Homura makes a point to prevent the event that made her Contract alongside preventing Madoka's. If not, go read Puella Magi Oriko Magica and learn of her last, desperate and failed attempt to prevent the rise of Kriemlid Gretchen.
She could also get a new short in the post-Godoka timeline, where she has once again Contracted and they talk of Madoka, and Oriko admits she was wrong about her - and then she tricks Homura in a deadly situation because now she knows of the coming of Homucifer and wants to kill Homura before it can happen, only to see Homura's wings and realize SHE caused it because she couldn't bring herself to trust Homura enough to warn her, with Kyubey telling her that if she had done so she would have shattered her Gem and foiled his plan - and Oriko replies with "Welcome to Homulilly's world".
Also, just for fun... Hitomi Magica timeline? One in which she single-handedly defeats Walpurgisnacht with her fists, but in the process she accidentally kills Madoka, prompting Homura to swear this one off too.