I worked with COBOL during the Y2K thing. Forget for a minute about the (very valid) downsides of startups: COBOL development in institutions such as banks is utterly boring. If, like me, you got into computers because you were fascinated by programming, run like hell from COBOL and forget the money argument. Run like hell whenever someone tells you "it's not that bad", like in the article. Nothing good can come from something introduced as not being "that bad".
If you're in this mostly for the money, then sure, learn COBOL.