My unicorn phone would be one that is both small enough to use with one hand (currently have a Zenfone 10 largely for this reason) and has a secondary camera lens that's a telephoto rather than an ultra ultra wide.
It bugs me that phones with a long lens are so comparatively rare, it's always just wide (verging on ultrawide) as default and when a second lens is added it's even wider again because people love distortions or taking photos in tiny rooms or something. Sometimes I just want to take a photo of something further away than a few metres and actually have it visible without zooming in, I'd even take a normal lens FoV as an improvement over ultrawide. Those phones that do have one tend to have it as a third lens and also tend to be huge, so get disqualified by the 'usable with one hand' criteria even before I reach the massively expensive part.
I'd also like an Instax back for the Hasselblad V series that was cheap enough that I could actually justify the cost of buying (say ~$200 AUD or less) though I will admit that's a pretty niche thing to be after.