The complexity in this space is difficult to overstate. We've been working on building solutions that integrate all of the disparate legacy banking technology into 1 logical application the bankers can use. Been going at this for almost a decade now.
Success in this space is extremely unlikely. We failed ~4 times but were encouraged by how close we got on that 4th try to give it a final go. Seems we have some traction this time. Watching other vendors (with far more resources than us) try to break into this space is quite amusing at this point.
The key to winning in banking with technology is to listen to the business. There is a LOT of contradictory bullshit in banking, and if you just use your developer intuition to build the domain model in isolation, you will fail as soon as the business gets involved. Outsourcing development of these integration products to a 3rd party is a guaranteed fail when working with these kinds of customers.
Expert mode is building a product that can work at 3+ banks at the same time. Darksouls mode is building one that can handle more than 5 jurisdictions.