I have worked in the banking industry. Building a better technology stack for a bank is possible. But you need to understand the current technology first, including how it got to where it is today.

You also need to understand the banking industry.

And you need to be focused on reliability. Twitter's reliability history is not adequate for a bank.

So do I think he can do this by himself? Not a flippin' chance. But I do think he could contribute some innovative ideas, if teamed up with people who have deep experience in the industry.