Glenn, I'm surprised no one has responded to this yet. But I'm always willing to offer an opinion :-)

You do know the Sophora will get huge eventually? (Seen the massive one at my nursery?) So that seems like it may not be an ideal choice to replace a 'Crimson Queen' Japanese maple. The Styrax japonicas are OK but sort of ho-hum.....they need rather attentive care for a few years to look good and tend be plagued with considerable winter dieback under even the best of conditions.

If it were my choice, I'd consider the obassia for sure; also perhaps a magnolia or flowering crab ('Sugar Tyme' is a gorgeous little tree and should be included in more gardens). Or, if you can provide sufficient water during summer, perhaps a Japanese stewartia.