I wondered if other banks that participate in a "Bank On" program might be willing to share their retention rate on the accounts opened through that program? Thanks.

That information would be anectdotal and heresay as far as I know. Retention might be reported by the Fed in the aggregate for each Bank On program, but not by individual bank.

That being said, the problem with the accounts opened by the unbanked or underbanked has been usage more than retention, in my opinion. Although I am sure both are a concern when determining how to make these accounts profitable.