I just found this forum through Google looking up companion guilds.
I really like the idea of keeping the Black Locus till something better comes along. This is what I'm doing actually!.. Well, with the Redbuds and Bayberry shrubs anyways.
I'm in zone 5 and Black Locus are extremely hardy, just an amazing tree all-round! Just an FYI you can graft or propagate the upper (past 5 scaffolding) branches and to produce thornless hybrids. I tried it last year with great outcome! I'm attempting to be as natural and native as I can for Central Indiana so I keep the natural thorns tho. They are great fuel wood aswell (since you have woods and maybe a wood-stove or fireplace).