On the basis of what I've seen so far I find it unlikely that Epstein actually cared much about establishing a "behavioral engineering institute". Baiting "thought leaders" by emailing them about big ideas and grand plans was his standard M/O, it seems. He must have sent hundreds if not thousands of such emails - Scott Aaronson got one[0], and with no disrespect intended to him he must be pretty far down the list of powerful people you'd want to collect.
[0] https://scottaaronson.blog/?p=9534