Question: I'm wondering if there is any news about a "Android Dev Phone 3"? Is an updated hardware of the "Android Dev Phone 2" that is coming soon? (probably an unlocked version of the Nexus One)

Answer: 
The Nexus One IS the unlocked version of the Nexus One! It's sim unlocked and the bootloader is unlocked.
There is no news or suggestion by Google, nor are there any leaks as of today.