Those might all be true and it's understandable why nobody wanted to support all that long term, but that doesn't mean people should abstain from developing their own languages and platforms, just because it lead to nasty code that one time at Fog Creek. And it's a "failure" that - from what I can tell - was a pretty good business decision at the time. But even if you discard that, even if you assert this was nothing but badness with no upside whatsoever, it would still be a learning experience.
When a rider falls off a horse, they have to make a decision: abandon the idea of horse riding ("riding your own horse rarely makes sense"), or apply that as a lesson to your skill set and re-mount. While there is nothing wrong in deciding that, upon reflection, horse riding was not for you, I think it's harmful to go out and announce to the community that riding your own horse rarely makes sense and should be left to the pros. Because what you're left with then is a world where the only riding is done by dressage performers.
(Sorry, that analogy got a bit out of hand, and admittedly I know nothing about horses, but I hope the point is still discernable)
Upon further reflection, I'd say that for the company in question, for that particular sector, having the query language available was a positive differentiator in the marketplace. I think it's clear Fogcreek's use of wasasbi was necissitated by the business and tech climate of the time. So clearly there are compellings reasons to go down this path.
I'd also say that languages are hard, runtimes are hard, languages and runtimes together are really hard. A decision to go down this path should be carefully considered, and not because a developer on staff read Parr's Antlr book and wants to try it out.
I work for a company that has the same thing. They have, basically, their own version of SQL. Clients can write scripts and import them. Lots of issues supporting it. I wonder how small the world is.
When a rider falls off a horse, they have to make a decision: abandon the idea of horse riding ("riding your own horse rarely makes sense"), or apply that as a lesson to your skill set and re-mount. While there is nothing wrong in deciding that, upon reflection, horse riding was not for you, I think it's harmful to go out and announce to the community that riding your own horse rarely makes sense and should be left to the pros. Because what you're left with then is a world where the only riding is done by dressage performers.
(Sorry, that analogy got a bit out of hand, and admittedly I know nothing about horses, but I hope the point is still discernable)