[TRY]

I like this discussion, because this is the way this conservative industry will go forward!

And this is perhaps the first and one of the major negative points: this industry is conservative! Like the aircraft industry (untill Airbus installed fly-by-wire!)
Maybe it just takes someone to do it in a logical way, on a medium-sized yacht.
Second negative fact is of course that the overall installation will become more complicated, suffice to draw a complete functional flow chart analysis.
Third may be the resistance of propulsion engines manufacturers. They can and will influence their (not always so knowledgable) clients to stick with the known-and-trusted technology.
The yards (unless they build on spec and with courage) will probable not want to experiment, and after all the client decides.

Conclusion: there may be much more reasons found against DE, it's easier to find negative arguments than positive!