It's already been done. Get yourself an N9 (same hardware as the lumia 800) or an N950 (most beautiful phone hardware I've ever had the chance to use but hard to come by as only a few thousand units were produced) and install nitdroid.
The problem is that the OS and hardware really go hand in hand. Installing a completely different OS than the one the hardware was designed for often results in a disappointing device. The N950 running Meego for example is still to this day what I would consider the pinnacle of hardware and software engineering when it comes to smartphones. It looks gorgeous, it feels amazing - no other smartphone I've ever used (and I've used many) comes close.
But install Android on it and it suddenly looks and feels like an unsightly brick. The way android looks like, the UI gestures, the way Android is meant to be used in general is different than Meego and it doesn't fit the hardware at all. It's loads of subtle and seemingly small details but the end result is a very unpleasant device.
I just mentioned this in another thread, but you could install Sailfish on the device, which is basically a fork of Meego, and use their Dalvik implementation to run Android Apps. At least, you will be able to do that when Sailfish is released.
The problem is that the OS and hardware really go hand in hand. Installing a completely different OS than the one the hardware was designed for often results in a disappointing device. The N950 running Meego for example is still to this day what I would consider the pinnacle of hardware and software engineering when it comes to smartphones. It looks gorgeous, it feels amazing - no other smartphone I've ever used (and I've used many) comes close.
But install Android on it and it suddenly looks and feels like an unsightly brick. The way android looks like, the UI gestures, the way Android is meant to be used in general is different than Meego and it doesn't fit the hardware at all. It's loads of subtle and seemingly small details but the end result is a very unpleasant device.