One of the big reason people pay to watch motorsports is for the noise and rumble of ICEs. It's no coincidente that Formula 1 kept loosing viewers and money the more cylinders they were reducing for the sake of "environmentally friendliness", even though the carbon emitted by their V12-V10 ICEs was dwarfed by the gargantuan amount of carbon released to move that circus across the continents all year.
So unless you ban ICEs in motorsports as well, I don't see how you can convince investors to spend big money in Formula-E development, considering how little viewership it generates, in oder for it to spawn cutting edge tech that can later trickle down to road cars like it was with F1 decades ago.