argh! did... did this just appear in the past couple of weeks? http://www.st.com/en/microcontrollers/stm32l496ve.html if not.. how the heck did we manage to miss it??
[edit] anyway... thought about it... it's too modern. pricing on taobao is higher than st's own distributors. plus, for an auto-reset/boot0 you still need an extra MCU/USB-UART IC to manage it, even though it has native OTG. arrangement would have to be similar to the due (dual OTG interfaces) and that's a big redesign (too big).
so... stick with this design for now. bit of a surprise on the STM32L471 datasheet: not only is it missing USB it's also missing an SPI-based bootloader. looks like there were a few screw-ups at ST during the fab / layout on this one. all the other ICs in this family/range have OTG and SPI-boot.. hmm....