A post on a Russsian smartphone forum hints towards the liklihood that Microsoft may be envisaging a massive change in the kernel source from Windows 8 onwards.
The document, which cannot be verified by secondary sources, claims that "Windows Phone 'Apollo' brings together platform parity with Windows 8, experience parity with Windows Phone 'Mango', and a set of new features and functionality developed for Windows Phone 'Apollo'."
Platform parity means, according to the poster, "the phone OS is now based on the Windows NT kernel instead of the Windows CE kernel. Windows Phone 'Apollo' uses the Core System from Windows 8, which is a minimal Windows system that boots, manages its hardware and resources, authenticates and communicates on a network, and can be managed at a basic level."
He adds, "the final significant changes of note are the adoption of ESENT, also known as Jet, for the database engine, and the managed-code runtime. Rather than using the .NET Compact Framework from Windows Phone 7, Windows Phone 'Apollo' uses the Core CLR produced by the Developer Division at Microsoft."
Apollo is the codename given to the followup to Mango (Windows Phone 7.5) and given the fact that Windows 8 can run rather decently on some antiquated hardware, it would not be surprising that some Windows 8 DNA will migrate to Windows Phone.