There is a reason Secure Digital killed off the MiniSD.
I was coming to that point... I wonder if in today's world they'd have felt the need to go down to MicroSD. Remember they were introduced in the days of ever decreasing phone sizes, before the smart phone took off in any meaningful way. I know PCB real estate is always valuable regardless of what size you're building to, but miniSD and microSD are just as thin as each other, and in today's world of tablets, phablets and generally rather large phones would the SD Association really feel the need to go that much smaller?