In fact "convenient" is just as much dependent on the usage as the range (actually, more so). Many people who may live in apartments that make it more difficult to charge at home have *free* chargers at their workplace (mine does). And in fact, plugin chargers mean you can charge it to some extent almost anywhere there is electricity (you can find supermarkets, shopping malls, even restaurants that have charging stations), unlike gasoline cars that make you go to a totally special purpose business - a gas station.
They won't be obsolete any more than a Toyota is obsolete when a new Ferrari comes out.
A Tesla with a 600 mile range WILL be a vey expensive car, since it needs a huge battery. The current P90D is well over $100K already, and it only gets 1/2 the range.
Seriously, then don't get one. Also don't get a Hummer if you live in a crowded city, or any car at all if you live on a small island. That's why there are 100's of car models out there. This was about solving one problem with electric cars, which is limited range.
Two is not equal to three, even for large values of two.