Among the concerns that were expressed in another similar thread were, less available overhead for modifying more power into it.
If like 99% of the folks out there, who will keep it stock, then the matter of available overhead won't matter; only one of possible durability.
Presumably, an engine that spends more of it's operating time at 85% of it's load capacity (more RPMs, higher cylinder pressures,) is not going to last as long as an engine that spends more of it's time operating at just 65% of it's load capacity.
But the 3 cylinder may have advancements in engineering and manufacturing design that could mitigate that presumption. After all, your current generation 4 cylinder will outlast the 1970s 8 cylinders while producing as much or more power.
Before passing judgement one way or the other, we'll just have to pay close attention to see what's happening with the current generation of 3 cylinders that are already out in the field.