Not much, I have no M5Stack myself, I was testing sharing SPI bus on my Wrover kit but the display and sd card are not sharing the spi bus on it 
I setup a repo here https://github.com/C47D/m5stack_sd_display_shared_spi
@mair.swartz was helping me with their M5Stack board and had an issue.
I can work again on this if you have a M5Stack board and can test for me, please let me know.