I wouldn't worry about it. If a user buys a 6 Plus or a 6 just and they find it unusable just return it.
I'm not certain it's as cut and dry as to which type of nand is going to cause problems.
I found the following:
"SLC NAND flash is typically rated at about 100 k cycles (Samsung OneNAND KFW4G16Q2M)
MLC NAND flash is typically rated at about 5?10 k cycles for medium-capacity applications (Samsung K9G8G08U0M) and 1?3 k cycles for high-capacity applications[citation needed]
TLC NAND flash is typically rated at about 1 k cycles (Samsung 840)
SLC floating-gate NOR flash has typical endurance rating of 100 k to 1 M cycles (Numonyx M58BW 100 k; Spansion S29CD016J 1,000 k)
MLC floating-gate NOR flash has typical endurance rating of 100 k cycles (Numonyx J3 flash)
However, by applying certain algorithms and design paradigms such as wear leveling and memory over-provisioning, the endurance of a storage system can be tuned to serve specific requirements.[45]"
So I feel as these algorithms etc being applied to a certain chip could make it fine for what it's being used for.
I'm sure there are iPhones 6's out there with TLC nand that are just fine.
Sent from my iPhone using Tapatalk