He is very INVESTED in their futures and the conception of Emma. I never thought of Charming and Rumple as related but I definitely see the start of a bro-mance between Charming and Rumple (and some interesting Holidays if they shared a grandson). The Dark One is clearly the president of the Snowing fanclub, so maybe there is motive besides the two making a savior: if the product of true love was really all he needed, couldn’t that have occurred centuries before Charming and Snow? What about this pair caught his attention or did he just see in the future that it was them, their daughter, ect.?
And now I really want a scene where Rumple and Charming train Henry to sword fight. I am doing great repressing this theory!