> eSign tech is a commodity
We learned this pretty quickly with our banking products. Having your own bundled, first-party e-sign features can help differentiate your product from other vendors, but if the only thing you are selling is e-sign, they probably won't look at you. We do have an in-house e-sign feature in our product now. We evaluated integration with Adobe & DocuSign, but their APIs were so far away from what we needed that we decided to DIY.
Consider this - what is a bank going to do with raw access to something approximating docusign APIs? They outsource everything. Their vendors are the ones who would be consuming something like this and then reselling it. Getting onto the QVL for a US financial institution (and staying there) is usually a monster battle if you are a new kid on the block.
If you still wanted to market this solution towards US financial institutions, I'd start with the vendors of those institutions. Companies like Jack Henry & Associates, FiServ, CSi, FIS, Harland Clarke, et. al.