I agree with Bob, the technology will need to advance to make electric viable. The analogy to portable power tools is a good one. I had planned to rebuild five 19.2V NiCad battery packs for my Porter Cable tools but I bought a cheap Lithium Ion driver to tide me over until I could do the rebuilds. I was so impressed that my plan now is to scrap the batteries and eventually the tools and replace all with LI. I'll hang on to the tools for a while to see if some enterprising individual comes up with LI replacement battery packs for old NiCad driven tools. I've also scrapped my corded hedge trimmer and am planning to scrap my gasoline weed trimmer/edger next spring in favor of LI driven tools.
In addition to range and power, cost is a big issue. For a sail boat, substituting batteries for ballast as an initial design rather than a retrofit just seems like the right way to go. I was really impressed with the Compac Electric option for the Horizon Cat, Eclipse etc. until I found out it was a $16K option. As much as I like the idea of electric done in that manner, those numbers just won't work. And I fail to see any real advantage to electric outboards whether purpose built or trolling conversions. Although I prefer an inboard for weight distribution and reducing stern clutter, Capt_Nemo's conclusion that a well tuned and maintained outboard, which will be trouble free if kept up, is a much better choice at this time than the electric outboard options.