I think you should let things play out as naturally as possible. It takes awhile to feel comfortable with polyamory situations for many people. If you asked him now about the future, he may think he will stick around for awhile but sees no long term future because that is what society teaches. However, after a few months, he may get a new perspective and really like how things are going and want to keep at it long term.
I think you should keep lines of communication open. Let your wife ask him if he wants to meet you and hang out for a BBQ or something. Keep it natural and not forced.