The auto industry is full of progress. Most of the time we know that new cars are just going to weigh more, be less engaging to drive, and basically be less good than the models they replace. Sometimes, though, innovations turn out better than expected.
Although I am sure is has been discussed to death, I still have an outstanding question about tuning an electric vehicle. Since there is no intake / exhaust cycle to worry about, all your standard engine upgrades will go out the window. What parts are we going to replace?
Battery packs for more juice and longer life?
Motors for more power?
Both seem incredibly expensive compared to a new intake.
But I see a worse scenario. What happens when the batteries and motors become so efficient that even the the most modest of vehicles will come with motors that could pump out the equivalent of 300-400 hp. Then all we could do is install an aftermarket dial that lets us adjust our EVO or STI from 50-500hp. No tuning, no wrenching, no grease.
A few hours later, stopcrazypp gave an informative response.
There's actually still a bunch of stuff you can replace in an EV: more powerful batteries, motor, inverter, controllers etc. It's all a matter of finding the bottleneck in the car and expanding it. Of course, that does mean low hanging fruit like an intake is off the table. But there's still plenty of wrenching available (see the EV drag racing scene). Although it's important to remember simple handling mods like suspension and brakes are still open.
As for your ending scenario, it's already happening. The Tesla Model S uses the same 300kW (402hp) motor in it's entire line-up. The bottleneck for the lower models are in the battery. That opens up the potential for tuning by using an aftermarket dial as you suggest. It's not very different than the easy tune of upping the boost in a turbo car.
Like MadisonSuicide says, EVs are like a car that's almost been tuned to perfection from the factory. It's because there is no trade-off between performance and efficiency like in an ICE car. You can buy the highest performance version of a EV (like the Model S Performance) and the efficiency is exactly the same (maybe even better than) as the lowest performance version.