Eh. I worked on IBM's COBOL compiler for four years or so, and I think you're overselling COBOL. COBOL is the best language for extending the functionality of critical legacy systems already written in COBOL. I have a soft spot for the language, in the same way you might for a puppy that is big-hearted but ultimately not very bright, but I can't imagine a greenfield project where COBOL is the right implementation choice. (Idiomatic COBOL does end up being surprisingly fast, mostly because the idioms were established in the 60s where things like "dynamic memory allocation" and "a call stack" were too expensive.)

The market for COBOL on .NET is limited by the fact that existing COBOL code is usually tightly integrated with the rest of the mainframe ecosystem (CICS, etc). The average COBOL shop has a low appetite for significant change. Even just recompiling the codebase with a newer version of the IBM compiler was often a big lift. (IIRC, when I left, COBOL 6.1 was generating code that was nearly twice as fast as COBOL 4.2 for CPU-bound code, although admittedly a lot of real-world COBOL isn't CPU-bound. It was still difficult to get people to migrate.) Anybody who wasn't change-averse and tied to the mainframe probably stopped being a COBOL shop years ago.

Edit to add: None of this is to say that Otterkit isn't a cool project! I just don't expect it to sweep through the world of banking.