I get the feeling that the desire for back-up in inner Wano will come in the form of the Whitebeard Pirates being in Wano, giving Yamato solid reason to finally sail out with no worry. I can see why it wasn’t suggested before since Marco prob figured Luffy could handle it, but upon realizing Luffy has no inner line of defense prepared, then that’s when Marco, Vista, and the others would pop in.