Do system font (TTF/OTF) forms of the Kepler Project fonts (kpfonts) exist?

You probably can create the OTF-files yourself. Get fontforge, open the *.pfb and whatever fontforge requires and try file/generate from the menu. Take care that you are allowed to write the new file into the same directory.

I did not try myself, but there is a chance it works.

Alexander

EDIT: It works in the way described above. Tried with one of the kpfonts.

Since 2020-06-20, an experimental OTF implementation of kpfonts is available at CTAN as kpfonts-otf.