Tankless heater will likely also require spark ignition, so that doesn't necessarily get you past the wiring reliability problems. Although I did use a tankless heater about 40 years ago that still had a pilot rather than spark.
My experience with the type (gas only, so far) is that there is not much flexibility in heat output, so you need to match the flow with the burner capacity. Too much water flowing (or too cold coming in) and it is not hot enough. Too little flow, and they can get to scalding temperatures very quickly. One that I've used actually produced steam from time to time before cutting out the flame on the safety.