Just FYI chains don't stretch over time. Chains are subject to stretch when load is applied but it's not something that changes over time. What people commonly refer to as "chain stretch" is caused by wear on the rollers both outside where they contact the cog/chainrings and on the inside where they contact the bushing (or in the case of a bushingless chain, the inner plates).
At this point I feel 1/8" chains, like thread on cogs, are simply a tradition thing. Given improvements in steel quality and manufacturing a 3/32" or even narrower chain can likely be stronger than a 1/8" chain could be 30+ years ago. Mountain bikes use 11 and 12 speed drive trains these days and see all kinds of extreme torque.