I asked this same question to one of the Microsoft program managers yesterday.
Answer said:
To be honest, lately I mainly use my phone to play Castle Siege, so I am really asking myself if I can risk it not working. That is a strong maybe...
Basically, ask yourself how much of an issue it's going to be if your phone becomes unusable or if a particular feature just doesn't work at all.
If there's any uncertainty, wait and see what the feedback is or ask questions so see if it's ok to jump.
Most likely, you'll just update the second you'll see there's an update available regardless of any concerns you might have.
Before you upgrade, make sure you know how to reset back to 8.1.