Microlith writes: Microsoft has updated their WHQL certification requirements for Windows 8, and placed specific restrictions on ARM platforms that will make it impossible to install non-Microsoft operating systems on ARM devices, and make it impossible to turn off or customize such security.
Choice quotes from the certification include from page 116, section 20: "On an ARM system, it is forbidden to enable Custom Mode. Only Standard Mode may be enable." which prevents users from customizing their security, and in section 21: "Disabling Secure MUST NOT be possible on ARM systems" to prevent you from booting any other OSes.
Microlith writes: According to Tom's Hardware, the bootloaders for the DROID X and DROID 2 will be encrypted and signed, much in the same fashion as the Motorola Milestone (GSM DROID) as well as their other handsets. If they cover their bases, unlike last time, this will bar owners from installing 3rd party ROMs.