There will be at least 3 more.
Festive in Death this year and 2 in 2015. She has said repeatedly she will let us know if and when she plans to end the series, so no doubt she plans to keep going at this point.
Plus only three years have gone by in the book's world despite real time being nearly 20 years and the number of books
(
Naked in Death starts in February 2058 and
Concealed takes place December 2060)