Looks like he basically wanted an Android version of the iPhone mini. But since he would need to get off-the-shelves components, he will be facing the same wall other Android companies are facing.
How's the Battery life? Even Apple couldn't magically make battery life good (ie. 12 mini). 13 mini fares better, but that's Apple having full control of the OS and SoC tuning. Snapdragon flagship SoCs have worse and worse performance per watt for anything higher than the Snapdragon 870. This is why Android phones are sporting 4500-5000mAh batteries. The whole set of components are just less efficient. Add on the OS that keeps more stuff running in the background, it will be a huge challenge. You cannot cheat physics. And no, going stock Android is not any better as many Android OEMs actually had to put more aggressive power management over stock Android to achieve good battery life.
And what's the actual demand? There's literally hardly any Android phones released in 2022 that is smaller than 6.4". Maybe the Galaxy S22. That's about it. Xiaomi just released their cheapest $100 phone in my country, the Redmi 10A, and that's already 6.53". People in general still think larger is better, and smaller means it has to be cheaper. Look at how many people here claiming that the 13 mini is overpriced. And there's a reason why larger phones are taking over. Going back to the previous point, battery life. To have better battery life, you have to have a larger battery. Also, more and more people use their smartphone as their do-everything device, including gaming and general entertainment. Larger screen thus is much more desirable.
I think going 5.4" might alienate many consumers. 6.1", aka the S22 size, might be able to entice more people while still being compact enough. TBH, after owning the S21 for a while, I do wish for a small-ish phone, so I really wish him the best. But I doubt he would go anywhere as the market has spoken.
Seriously, no Android phones released in 2022 that is smaller than 6.4" other than the Galaxy S22. Last year, there were some, but really nothing this year. Even Huawei pushed its P50 to 6.5" (from 6.1" of the P40). If the Chinese OEMs are not even interested (and they do throw everything on the wall to see what sticks), maybe the market is just too small.