I think most current models will experience some other hardware failure before their flash memory really starts to wear out. Most SSD failures that consumers experience are catastrophic firmware bugs that are largely unrelated to flash memory endurance, which is why they seem unpredictable. Assuming Apple's homegrown SSD controller technology has been rigorously tested against what their own OS will do to the drive, they should be no more prone to such failures than top-tier retail SSD brands. Barring that failure mode, the batteries, displays, discrete GPUs and DRAM probably all have expected lifespans that are no longer than the SSDs.