Unfortunately still relevant... I can't count the number of times when investors are pushing on a CEO which in turn starts to worry about scalability & ask the team if Cassandra isn't a better fit etc (when the whole data can indeed be kept in memory or some midsize USB key).
Cassandra is not limited to use cases that need to scale-out, but it also excells at stuff that needs to be always-on, regardless of data size. Sure, you can do many nice things with data in memory or on a midsize USB key, but when your centralized hardware fails, you have a problem and in the best case you restore from a backup - and during downtime your customers go to your competition.
