The fact that there is a COBOL 2022 standard (yes, it's still being maintained) should have given enough of a clue that COBOL doesn't run only on legacy mainframes and tape drives anymore.
Sure, there are still companies using COBOL 85, but that's not the fault of the language. You wouldn't blame Java itself if companies used a version from the 90s intead of a newer and better version.
I find it quite absurd when people hate on COBOL based on its version from the 80s, while ignoring it's newer standards.
I don't see this as a product that needs to attract customers. It's free and open source, anyone can use it.
There is an enormous amount of new COBOL being written even for mainframes.
There is almost certainly a large market for COBOL on .NET if it managed to replicate some of the functionality IBM added on top of the standard.
A better term for COBOL (and mainframes for that matter) would be niche, not legacy. It's the best language for a very particular subset of business problems, and there hasn't really been much attempt to replicate that functionality by newer languages, and so COBOL remains in use. There simply is not much overlap between the folks coming out of school interested in language design/theory and those that are aware of COBOLs continued dominance in certain types of business.
It's also ruthlessly efficient compared to something like Java or .NET, and even beats out C by a wide margin in certain scenarios. That isn't as important if your not laying mainframe licensing fees, but it is a common headache that makes migration to some of the current virtualization based modernization platforms a headache.
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 Even just recompiling the codebase with a newer version of the IBM compiler was often a big lift.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.
Can you give an example of "services provided by the mainframe OS/environment" that could be practically/scalably emulated on a microcomputer architecture using library shims? Because those honestly sound like the sorts of things one might want to use even for non-legacy purposes :)
https://aws-quickstart.s3.amazonaws.com/quickstart-microfocu...
It's pretty amazing, big companies make these migrations on important systems. There are 10's (or 100's maybe) of billions of lines of COBOL still being deployed and companies move them into a cloud (ie aws etc, x86 + cloud services) environment for various purposes.