I’m a bit curious about what the PL/SQL is being migrated to: you didn’t say. If it’s another proprietry format (albeit Ingres’ and therefore “free”) then who cares? Ok, less licence money but still not that good. I beleive the two proprietry languages aren’t that far apart anyway.
If it’s into Java or something else that is the lowest common denominator (albeit boring) I can see the point. I did once look at such a tool myself but had no time. You could also put it back into Oracle if you wanted to, which might be interesting if the app moved on and you needed to go back there; making the server-side app database agnostic is a very useful thing not just limited to Ingres.
Of course, MySQL has only just got database procedures and they are still beta (and pretty tame). Again a neutral language would be more use here.
Have you come across the Oracle wrap utility that can be used to pre-compile your PL/SQL and make it impossible to read? There are a lot of people out there who’d pay serious cash for a converter that could turn that output back into anything human-readable.