Rolex is kind of like Smith & Wesson: anything is possible, models don’t change often, and the most visible changes are usually cosmetic. That said, from a pure timepiece standpoint, Rolexes have consistently improved over the years. They’re more shock-resistant and durable in general, the bracelets are better, etc. Unfortunately, from an appearance standpoint, they’ve gotten beefier, shinier, less graceful, and generally more blinged-out as time has gone on—just compare a 1016 to the current Explorer or compare a 1675 GMT to the Batman and you’ll see what I mean.
If you like a particular model, chances are that it will be available for decades to come. You may not be able to buy a Batman GMT II from an authorized dealer 5 years from now, but plenty of collectors will have them for sale in near-new condition and prices won't be completely intolerable.
Okie John