You will see parts available for the 01-17 GL1800 and F6B for many years, there are many, many bikes out there. After market manufacturers only stop supporting when the sales of the accessories drop to low levels.

I talked to Big Bike Parts last Friday, they will have certain parts available for the new 18 models out as soon as two weeks after the bikes are out. They are getting the first bike available in their area. Obviously there are a lot other parts that will take several months to get out.