1. Windows phone is currently not suited for mid-range phones, and wont be till the next version. However, long term plan is to definitely push Windows phone towards a wide spectrum of price points and replace Symbian. This will take 2-3 years.
2. For now, till the time WP is ready for mid-range, Symbian is still alive. New devices are still coming out, primarily targeted at mid-range. Nokia aims to sell around another 100 million symbian devices, all of which will run Qt. I would expect Symbian sales to continue for another 7-10 quarters.
3. Even below smartphones, the so-called "feature phones", the space is evolving to accomodate even smarter devices. Nokia sees a big opportunity in making the sub-$100 devices smarter (we are talking unlocked prices here, not american subsidized ones). Those price points will be achieved with Nokia's own software stack. Currently, this includes S40 where you can write applications using J2ME. This will be evolved so that in the future you can write applications for such devices using Qt which is vastly better than J2ME.
As an example of this space, Nokia recently released a sub-$100 small touchscreen featurephone with inbuilt offline Nokia Maps. Nokia calls this low-end effort as its connect "the next billion" effort. Likely Qt will debut on these devices next year, when Qt 5 will be ready.
Qt and Swipe UI is their long-term strategy. WP is short-term. Low-end is getting more capable and Nokia aims to enable smartphone capabilities for the 'next billion'. That's the disruption.
