Funnily enough, I believe he could be a very good appointment. He's had a somewhat nomadic career so far in management, but with the right backing in terms of finance and support, I think he could do a very good job for us over 3-5 years, and if more successful than anticipated then over a longer period.
I'd say we'd definitely be Europa League contenders under him, and depending on recruitment we should be contenders for the CL. Ranieri has proven there are no longer limitations if you hit upon a winning formula - I don't see an obvious reason why Koeman couldn't get pretty close to what Ranieri has achieved. From what I hear, Moshiri really likes the guy and his ideas, which in terms of building something over time seems a good starting point.