One potential use for non-DNA/RNA-based life: a fail-safe for a useful but potentially-dangerous synthetic organism. If you have a synthetic organism that is us

One potential use for non-DNA/RNA-based life: a fail-safe for a useful but potentially-dangerous synthetic organism. If you have a synthetic organism that is useful in controlled circumstances but could cause a catastrophe if released the the outside world, you could make it use an XNA instead of DNA (and/or RNA), and ensure that it lacks the biosynthetic pathways needed to synthesize the building blocks. Then the organism will be utterly dependent on you providing it with the required XNA building blocks, and will be unable to survive if it is accidentally released.