Why Ada Isn't Popular (2014) : Everyone outside the DoD wrote it off as dead in 1998.
My previous employer chose C over Ada for all their projects, and they paid for it when you looked at the overruns and additional moneys spent on testing and analysis tools that Ada provides as a language feature.
It would be interesting to have a version of SPIN [0] using this. This [1] looks really fresh. And I love the idea of creating new languages out of a subset. Almost all teams create an ad hoc language subset, formalizing it can be really powerful.
The main thing I remember is that it was very annoying to be fixing indentation issues on a terminal text editor, although learning about packages was very cool. Irrationally, the indentation strictness annoys me in modern languages like Python, too :) that, and using := instead of = felt like a waste!