In terms of the next 5 years or so, I'd put Milwaukee's odds fairly low -- 10% to 20%. The city has solid hockey history and a decent potential venue (although the Bradley Center has its share of critics), but faces five major obstacles:
A) Lack of any immediately viable ownership group (could change quickly, though)
B) Relatively small population
C) Proximity to Chicago
D) Unremarkable support of current pro teams
E) Behind Seattle, Quebec and probably Portland in Bettman's pecking order
Milwaukee ranks 56th in North America in metro population; that's well below Seattle (23rd), Portland (35th) and even KC (43rd). Quebec is significantly smaller but it has the Canadian hockey aura.
Also, the Brewers rank a mediocre 17th in MLB in attendance and the Admirals a middle-of-the-pack 14th in AHL in attendance -- more crucially, behind that of other prospective expansion locations like Providence, RI (3rd), San Antonio, TX (6th), Charlotte, NC (8th) and northern Toronto (9th).
I personally feel that the NHL could succeed in Milwaukee, though it may be a riskier place than Quebec, Hamilton or Seattle. However, I don't see it happening anytime soon until the city can garner more attention and interest about an expansion/relocation bid.
Hope that answers your question and gives a general description of Milwaukee's situation.