The game changer in the buying public's minds will come many years before the manufacturing capacity is there to provide it. Right now there are about 80 million passenger cars about about 15 million light trucks manufactured. Call it a round 100 million for convenience. The world's entire production of BEVs is about 100,000. That's 0.1% of total passenger vehicle production and it's consuming all the batteries the existing batteries can make. The Gigafactory is going to double the total Li-Ion battery production of the planet and provide capacity for about 600,000 long range BEVs a year. With the rest of world production, that's about 700,000 a year. Not even to 1% of total production yet.
The Model 3 could possibly set the public's imagination alight and demand could be very high. There are a number of BEVs on the drawing board out there, but with the current capacity of battery production, all of those vehicles will be limited production, even if there is a big demand for them. There is no evidence anybody is building another Gigafactory which would be needed to mass produce more EVs.
Tesla is fast tracking the Gigafactory and doing things in their own fast and flexible way. GM or Toyota couldn't build a Gigafactory and get it going fast enough and neither could their suppliers. Big, well established companies have procedures laid in stone that slow down any major capital expenditures. If it's between an automaker and a supplier, the lawyers are going to spend a year arguing the fine details on the supply contract. The supplier doesn't want the car company to pull out and the car company doesn't want the supplier to flake out on them and not supply them with their parts.
If the Model 3 takes off, Tesla might start work on a second Gigafactory right away, but realistically the capacity to get enough batteries to get over 1% of car production is at least 5 years out. And that's just the second factory. The world would need about 200 Gigafactories to completely convert car production to EVs. That doesn't count the infrastructure changes needed to support EVs. Most people with EVs charge at home now, but close to half the world's car owners don't have that ability because they don't have a garage, live in an apartment, or their house doesn't have the wiring to support it. Power utilities need the extra capacity for charging, and every company building EVs needs something to support long distance travel.
I think the likely technology that will serve as a stopgap will be biofuels. In the US, most vehicle ethanol is made from the byproduct of making animal feed from corn. It was just thrown away before the idea of biofuel came along. And there are a lot of other waste products that could be turned into biofuels. Most cars made in the last 20 years can be easily made to support flex fuels (almost all have it built into the firmware, most car companies just disable it outside of Brazil where it's mandatory) and biofuels can be sold at the same stations that sell gas now.
EVs are the long term solution, but the infrastructure to build and support them won't be complete for decades. It's a massive switch over that requires massive capital investment to get all car production converted.
With new technologies there is always the question of scalability. Some scale easily, some won't scale at all, and some will scale, but it will take a massive effort. EVs will scale, but it's in the massive effort category. Something like smart phones scaled very easily because they could start out working with the existing cellular networks and really didn't require major factory retooling, major changes to supply chains, or major changes to the support network.