Yes, it would be odd for Terraria to fund solely something they don't use even if it's more relevant for replacing Unity. I was actually involved in an enginee

Yes, it would be odd for Terraria to fund solely something they don't use even if it's more relevant for replacing Unity. I was actually involved in an engineering software package that used XNA. It was resurrected a few years ago after close to a decade on ice. We were sure glad that FNA existed because Microsoft had dropped XNA like a hot potato. Yeah, I wouldn't trust them again either.