Might as well just call up David Poile and see what he wants for Pekka Rinne...
Allen isn't the best, but like it or not he's going to be Blue next season. I'd rather focus on upgrading the roster around him so we can start out scoring whatever softies he gives up, because in my opinion the Blues moving him especially for the likes of Lehner, Markstrom, or some of the other suggestions is as unlikely as the Preds trading away Rinne.
Only way I see us moving him is if the Blues had determined they are in a "rebuild" and were selling him to a team that desperately needs a goaltender. Not many teams fit the bill in that category. That being said if Husso's development continues on track and Seattle for example enters the league in 2 years or so, maybe we expose him in the expansion draft at that point and shed him through that method, but with 3 years left on a 4 year contract and given how high management and the coaching staff are on getting him going, they are not going to move him for anything that's on par with what we've already got.