From what I've heard Icelandair is considering becoming an All-757 airline. They only have a few 737-400s, they recently replaced their 737F with a 757PF, and hold orders for further 757-200s and 757-300s.
For such a small airline operating a single type, which is as versatile and dynamic on both long and short routes as thr 757 makes sense for Icelandair.
I stronly doubt you'll see a widebody in Icelandair colours anytime soon! If it is, it'll probably be a 767 anyway