The cleanest solution would be if the babel authors would include it as a option for blocks that can produce SVG output. The solution I give here uses a :post option that invokes another src code block filtering the results of the current block. This is a powerful technique, but it can also make the code more difficult to read and debug.
First I define the postFileToIclude filter function to use in the later code block, and I test it by giving it a file link string (someplot.svg) explicitely.
#+HEADER: :var text="[[file:someplot.svg]]"
#+BEGIN_SRC elisp :results value raw drawer
(cl-assert text nil "PostFileToInclude received nil instead of text ")
(if (re-search-forward org-any-link-re nil t)
(progn (let ((fname (match-string 2)))
(format "#+INCLUDE: \"%s\" export html" fname))
(error "PostFileToInclude: Was not able to find link in output"))
#+INCLUDE: "file:someplot.svg" export html
Now we use this function in a :post argument for filtering your src block. One also needs to add a :results option, so that the output is not in an example environment. I also add a drawer, so that repeated executions will be able to correctly replace the results of previous evaluations.
#+BEGIN_SRC gnuplot :file example-plot.svg :exports code :post postFileToInclude :results raw drawer
#+INCLUDE: "file:example-plot.svg" export html