Coming back to the S4, it should be possible to have Nvidia design a WP8 compatible SOC. Also Huawei could do such a chip. I am starting to think that the whole WP project is a ship with no one at the helm.
It is up to Microsoft to add the Software support. You'll notice that Qualcomm was the launch partner, which doesn't rule out them allowing other SoC in the future.
ST-Ericsson - NOKIA SELECTS ST-ERICSSON AS SUPPLIER FOR FUTURE WINDOWS PHONE DEVICES
NVIDIA - Nvidia Going 'Grey' for Windows Phone?
Wouldn't be surprised if we saw support for different chipsets for either WP8.5 or in the Spring update. Consider that Windows RT (same kernel as WP8) already supports NVIDIA's Tegra 3 and TI's OMAP.
