MUMPS still sees a lot of active use today -- and MUMPS databases store data in plaintext, in ways that tend to be pretty well-documented and relatively easy to understand. EBCDIC, Betamax, laserdisc, Zip drives, and HD-DVD are probably better examples.

With all those positives, would you use it?

Didn't you say that MUMPS is an obsolete or generally weird format, not that it's something you wouldn't use?

But yes, I use it, both professionally and personally. Legacy MUMPS is not pleasant -- the VA's code looks like someone left their telegraph out in the rain -- but the language is astonishingly good at string-handling, mostly due to certain constructs that make it very hard to translate into normal languages.