No SPI - is very bad. Use an SD card (speed 50) or eMMC (speed 125) , if you have USB 3 (speed 340), to work - you need to be an idiot. At the same time, u-boot placement is possible only on SD\eMMC\SPI and therefore for the system to work with USB, you will have to have either an SD card (all SD cards are complete crap in speed and reliability and I generally consider them only as temporary media , such as CD\DVD on a PC), or buy an expensive branded EMMC module (almost 15$ for 8Gb), just for the sake of starting the system from USB. HK needs to be added before mass release SPI (only 4Mb is enough) and make it the main carrier for u-boot placement.