When forecasting the % of fleet that is EV, you need to start first with a forecast of % new sales, then look at retirements. Even if EV sales were 90% of total vehicle sales in 2013, it would be 5+ years before EVs were 50% of the fleet. Cars are durable goods.
That would be true if all remains the same as today. But things change.
If conversion kits become economically viable compare to keeping the ICE, the outcome may be very different.
Think about solar city business model, savings by replacing energy source. This model can be easily adapted for the ICE/Electric conversions...