I would think they mean "plunge bases for trim routers" - not the plunge base for the 1617.
The Bosch Colt trim router has a plunge base, for example: https://smile.amazon.com/Bosch-PR011-Router-PR20EVS-Routers/dp/B009ZQUB5O/
You can get a ]two-handled plunge base](https://www.amazon.com/Bosch-PR011-Router-PR20EVS-Routers/dp/B009ZQUB5O/ref=sr_1_5?ie=UTF8&qid=1464842679&sr=8-5&keywords=bosch+colt+router) for the Colt routers. There are also two-handled fixed bases available too, like this one (although I've seen others that aren't nearly as ugly.) A two-handed fixed base like that would actually be a simple DIY project if someone was so inclined.
Bosch actually sells the Colt in a kit with the plunge base, but at that price (almost $200) I feel like a buyer should just step up to a full size router instead.