This time around we have a decade plus of virtualization experience and specialized silicon in many (most?) modern processors like Intel VT-i/x/d and AMD-V. We no longer have to try to emulate kernel code or implement interfaces like POSIX or WINE on top of other kernels that inevitably lead to impedance mismatches between very different archirectures.
For example, modern virtual machine software like Parallels and VMWare Workstation allow for "unity" modes where the guest OS window manager is hijacked so that each window can be rendered onto the host without the rest of the guest desktop interface. If you're running the guest kernel "side by side" with the host as a virtual machine, you can focus on drivers that bridge the two operating systems (filesystem, network, window manager, etc.) and make it seamless instead of trying to shoehorn a low level emulated interface into a system that may not be ergonomic for that task.
For example, modern virtual machine software like Parallels and VMWare Workstation allow for "unity" modes where the guest OS window manager is hijacked so that each window can be rendered onto the host without the rest of the guest desktop interface. If you're running the guest kernel "side by side" with the host as a virtual machine, you can focus on drivers that bridge the two operating systems (filesystem, network, window manager, etc.) and make it seamless instead of trying to shoehorn a low level emulated interface into a system that may not be ergonomic for that task.