I would say that open-source is a "long road" for financial institutions, in general, even if it is not for rational reasons. They are concerned about crooks finding vulnerabilities they can exploit in open codebases, for example, and they are concerned about always having a 'throat to choke' in the form of a very solid support services provider. Only when an open-source project is huge and very well-supported by several large systems companies do most institutions start to come around. Linux, for example, has been hugely embraced by financial institutions...but most of that acceptance took place only after Red Hat, IBM (etc. etc.) were around for services/support contracts. Financial institutions do NOT like risk. They absolutely HATE risk. A guy in a garage is a huge risk for them, even if you do develop a killer product/service.

As a 'guy in a garage,' I'm not sure a financial messaging product would be my choice to focus on, open-source or not. It is a rather difficult market even for well-financed companies with teams of programmers and salespeople. Isn't there another market where your skills might be better leveraged?

You are right. I have the same impressions about the conservativeness of the financial institutions. This is one of the ideas I am evaluating now, counting the pros and cons. I can focus on other "messaging" areas not necessarily related to financial messaging.