How would this be integrated into the standard SPI lib so that you could use multiple SPI devices at once without them all or none having to use DMA?
Strikes me as a pity that you need to go the DMA route to get performance that is equivalent to a simple FIFO buffer as found on the Teensy chip. Seems like a lot of added complexity with all the attendent issues just to get to a baseline of a reasonably efficient SPI performance.
I gather from what you've written there would be little or no point in terms of a speed benefit in doing DMA SPI for the Teensy 3, for example?
Do you think there is really no hope to get the poor Due SPI performance improved to any significant degree without resorting to DMA?