20-Year Prospect
You can't say this with many careers, but there's a 0% chance of CSIs becoming obsolete. CSIs just don't have to worry about their jobs going the way of answering machines and phone booths (does anyone know where Superman changes these days?). Technology may change how things are done, but we're still always going to need those same things done.
It also just wouldn't be cost effective to send food inspection jobs overseas, so local CSIs will always be needed. Unless lightsabers for home use make it possible to kill, cut, and cook a meal instantly...but even then, most people's backyards just aren't set up for that kind of thing.