Tesla produced ~80,000 cars last year, Ford produced 6.7-million. From a purely numbers perspective its pretty much inconceivable that Tesla will approach Ford for decades, obviously Ford also has a correspondingly larger number of assets and there is considerably more risk in Tesla's future than Fords.
Actually it's is quite conceivable they will overtake Ford on *just* volume of cars by the mid-2020's. If all goes according to plan, Tesla will produce 1 million cars per year by 2020. Note that they have over 400,000 reservations for the model 3. That is unprecedented in modern automotive history so it is likely that the demand for the Model 3 is present in the market. After reaching the million per year rate, Tesla will have to start replicating it's production plants and gigafactories around the world and move down manufacturing scaling laws. How well they will do depends on how good their Engineering team is. So far they seem pretty damn good.
Look at it this way. There is a Market for 100 million cars per year world-wide. By the end of the next year Tesla will be the only car manufacturer capable of producing 500K - 1 million electric cars per year. There is a lot of demand for Electric cars. If they pull off autonomous driving there will be an even bigger demand. Tesla is is far and away the leader in electric cars with a potential market over 100 times bigger than their projected volume in 2020. Is Ford going to grow their volume much above 6.7 million cars per year? Not much, if at at all. Will Tesla? They have the chance. Hence the Capitalization.