So unless I'm just misunderstanding, right now SAM seems to only be able to target other missiles. It would be nice if there was a way to specify other entities, like the Wither or an IaF dragon, whose flight normally makes hitting them with a missile extremely difficult. If this is currently possible/already planned then I apologize, I looked over the wiki and configs and didn't find anything mentioning this.

Its half planned, falls outside of the scope as the surface-air-missiles were originally anti-ballistic missiles. So we have kept them focused on killing other missiles. That said the code can support it easily. As would just take the radar or SAM to mark it as a threat. I've been tempted to do it for those annoying sleep flying fish.