There's lots of keyboards over ten years old now that are in demand, and synth technology really hasn't made any quantum leaps forward lately so current instruments will certainly have a useful life of ten years or more, in capable hands of course.

Arranger keyboards are probably the most common type of electronic keyboard in the world currently. They aren't going away, but the so-called "pro models" might. I don't think they've been marketed in a way that attracts pro players and they are often too sophisticated and expensive for casual players. Yamaha has broken a little of the ice by including chord-recognition in the arpeggiator function of the Motif ES, but I think we're awaiting the next advance in arrangers before we can say whether pros will ever take to arrangers. That next step is probably arranger-type functions that work not only with MIDI but with MP3's, WAV files, and "Acidized" loops. We'll certainly see softsynths become more commonplace so in the next ten years I see many of us moving into softsynth host instruments, which will take us away from the Y/K/R relationships we've all come to love/hate. Once we integrate soft arranger programs with softsynths and reliable host instruments, it won't be a question of whether arranger keyboards stop being made but whether they will simply become old fashioned.