I guess they forget something important, why should people switch from their current OS which they're already comfortable, and MORE IMPORTANTLY, they already invested their $$$ on the apps. Switching platform means loosing almost everything.
What's a good reason to switch?
Is WP good enough? For simplicity, smoothness, no fancy homescreen, customization, there's iOS.
For cuztomization, flexibility, power, choices, etc. there's Android.
Where will WP8 stand? Current WP7.5 stand more like alongside with iOS, it's no competition for Android.
At least Symbian offers customization, flexibility, but the OS features itself lacking far behind.

Even if WP8 really become successful, there's another BIG Question: Why Nokia?
With it's current state, people are loosing their hope, trust, confidence. You go to any malls, you used to see Nokia here, Nokia there, now it's Samseng here and Samseng there.
Samseng triumphs PaiKia (aka Nokia)
Why Samseng is so successful, all thanks to PaiKia, most of their users are from PaiKia, converted to Samseng.
Choosing WP is their biggest mistake.

Can they climb back up now that they're at the very bottom? As a user/customer, of course I do, it's good to see more competition and also Nokia coming back up. But it seems they're getting worst everyday at fast pace.
You go to the mall, you see Samseng store is crowded and full, and Nokia Store, seems always can even hear mosquito sound... ok, that exaggeration, but you can see the big difference, and many people who visit Nokia Store are those still loyal to Nokia brand that aren't really looking for a smartphone or doesn't really know much about smartphone thing. Some may buy the Lumia, but how many of them will "stay"?
The worst thing that could happen is for them to find out the problem and weakness of Lumia (or WP) and then give up. Now they have a bad impression on Lumia (or WP), and this is not a good thing. Just as how people are disappointed and given up Symbian, will they want to "re-try" or give 2nd chance to  Symbian again next time? Take the risk? Why should they?
During S2 era, it was OK already.
In you say Symbian replacement, it's already a great replacement for Symbian since quite long ago.

You can honestly consider Samseng S3 or Note2 (if you don't mind the size). Been using SEX Pro for some time, honestly speaking, Sony's version Android a failure and their older devices lacks of RAM and internal storage, was a horrible experience. For Android, make sure you get a decent spec hardware with enough internal storage for apps, micro-SD support and RAM.
Besides in term of OS, Samseng did much better than Sony, in default stock mode, there's many shortcuts in the drop down menu, there's S-Voice, there's many nice and useful feature I wished it was available on the Sony.
Image quality, it may not be as good as 808 PureView, but in terms of usability, it's actually much better, it's faster and more responsive, image quality is decent and very good for mobile phone category.