In JavaScript land, postgres bigints deserialize as strings. Is your application resilient to this? Are your downstream customers ready to handle that sort of schema change?
Depends on the lib. Max safe int size is like 9 quadrillion. You can safely deserialize serial bigints to this without ever worrying about hitting that limit in many domains.
2^53, to be precise. If your application involves assigning a unique identifier to every ant on the planet Earth (approx. 10^15 ≈ 2^50), you might need to think about this. Otherwise, I wouldn't worry about it.