Exactly; I've seen a number of instances now of people pushing the hip new technology, but jumping ship (i.e. getting promoted, a new job, or a different assignment) shortly before or after the shiny new thing was "done".

In one case, ten years later, the company is still struggling to maintain their Scala applications in an environment where there's barely any Scala developers (and who charge a premium because it's specialist work), while the main author(s) went on to work at the company behind Scala itself. I'm sure Scala is great for specific use cases (just like every other non-top-10 language out there) but please, think very carefully before trying to build your company on top of it.