I've never looked at those chips before. They'd be an useful addition to the library. 
My plan's to add support for ATMEL's flash chips sometime in the future and support for Spansion's flash chips would make it more widely useful.
I've never seen QSPI being used in any other libraries either. The Winbond Chips support DSPI and QSPI. Its something I'd like to integrate into the library if I can.
P.S. Is your code on Github? I'd love to get a look at it if that's ok