I can think of 3 problems. If these 3 problems can't be solved, WoA doesn't help.
1. Mobile apps. Actually, it's not about the apps that suitable for mobile, but the apps that currently only available on mobile and you can't complete the task with your PC. Maybe you need that to control your smart home device, to participate some event, to check news, or to play video games (e.g., Nintendo Switch). Nowadays more and more services only available on mobile apps, and they don't even have web portal. WoA can only replicate desktop experience, but that's still not enough.
I know some may say the device is for a specific market and it's ok to not having those apps. But is that true? For any individual (other than die-hard fan), that means they need another phone to complete the everyday tasks. Meanwhile, the competitors are also working on docking experience. If there's limitation set for WoA (e.g., only selected apps from Store, like WinS), it's possible that even for the specific market, competitors have better overall experiences.
2. Stability. W10M is so buggy, and the API is so limited and broken. Sometimes I could understand why devs abandon their app or don't fix some issue, not because they are lazy, but because they can't do that: either there's no such API, or the function they depends on is buggy on W10M. I don't think WoA can fix that as well, if not introducing more bugs.
3. Trust. How could devs and customers trust yet another reboot? If it's just the first or second times, it's ok. But this is the 4th time. I assume it will take really great effect to build the trust again this time.
I really hope that besides WoA, there's Android side-load app support (with limitation, e.g., number of apps), so at least problem 1 could really get fixed.