First paragraph, agree completely that those teams won't be looking for goaltending help. Even if Murray and Holtby are struggling, they have two Cups and one Cup respectively, no way they bring anyone aboard to threaten their jobs.
Calgary would be the team most interested I would think. Rittich has done well this season, but the playoffs are a completely different thing, and he has no playoff experience. They do have Smith, who hasn't played a playoff game since 2012, but he's a good veteran presence to help Rittich, and can step in if need be. If they traded for Howard, he would end up in the same role as Smith is currently. Vancouver is probably fine rolling with Markstrom, since they aren't contenders. NYI has Lehner and Griess, I figure they are set.
Unless a playoff team suffers an injury, like you said, it will be difficult to trade Howard, especially for what Holland wants in return. As for the outside teams, Edmonton just signed Koskinen for three years, he's their starter, bringing Howard aboard is unnecessary as Koskinen has proved mostly capable and they aren't making the playoffs anyways. Don't know much about Colorado's sitch, but Carolina has an insanely cheap tandem in Curt Mac and Mrazek, and they haven't hinted at bringing anyone else aboard. Seem confident in Mac as the starter. Although they are only a couple points out of the last WC spot, so that may change in the next month. If they did trade for Howard, i'd want Mac as part of the package in return, sign him for a couple years to split time with Bernier.