The new Amazon Kindle Fire HD 7” has a locked boot loader according to the XDA forums. so that makes a big crush when comes to custom ROM support ( as the bootloader is responsible for checking the firmware’s signature before a device boots ) so when the boot loader finds something wrong then the device won’t boot.
So this makes a clear statement that Amazon is really focused on their product and future income through ads as the subsidized versions might not get an easy unlock. as the Device use high security features offered by Texas Instruments’ OMAP processors. so there is much hard for an unlock, but still there might be some way’s in future but not that easy way for a quick upgrade to open Android versions like Latest Jelly Bean.
(note : Amazon has already make a stament that the Kindle Fire HD 7 core is based on the Android ICS version . but now it proven to be harder to unlock so the Nexus 7 is more advantage version in my opinion if you prefer to do some fun with your Tablet.)
[ source : XDA forums ]