If we're talking about 100x longer than 20 years, it won't matter to most people. Looks like in the XS write endurance testing thread a 120GB 840 was able to handle about 425TB of writes before going belly up. A 500GB drive should have about 4x the endurance, so 1.7PB of total writes. As an OS drive a person would probably write 5-15GB/day to it, let's say 20GB just to be safe. At that rate it would be 233 years before you exhaust all the writes on the drive.
Not saying I'd stick one in a server or subject it to some other very demanding workload, but for home use even TLC is plenty good enough. Especially larger capacities like 250GB and 500GB since they have so many cells to spread wear over.
People focus too much on P/E cycles. What matters is how long they actually last in the real world with the usage you will put it through. Plus more than just P/E rating affects write endurance, 840s have more over-provisioning for example to help offset the lower P/E rating for TLC NAND.