It's already mainstream. See the cars out and about everyday. Just about everyone is using electric weedeaters and power tools now. For an outboard it makes even more since just for the quite operation and the fact it can sit in your garage all winter and be ready to go with no issues come spring.Gotta get better battery technology and faster charging before it hits mainstream.
AND the power generation and transmission issue... Need twice the copper we have mined since WWII, and double the power generation currently in use to power the "required" lectric vehicles twixt now and 2035.....
Battery technology now is absolutely amazing compared to just a few years ago and only getting better at lightning fast rates.