Lincoln's iconic Town Car (pictured on the right) was a fixture in American fleets for a very long time. For decades, the car was synonymous with the American (and, to some extent, the world's) vision of "the limo". It was also extremely popular as a hired car, its comfortable ride and incredible interior room making it uniquely suited for the job.
In 2011, Lincoln decided to move on from the Town Car, a decision stemming from parent company Ford's decision to end the Panther platform altogether (thus putting an end to the legendary Crown Victoria as well). This has left a hole in the market place that hasn't quite been filled. The MKS has been adopted as a livery car by many operators, but doesn't have the unique qualities (size, tremendously soft ride, etc) that made the Town Car so suitable for that role. I suppose it does the job, though.
As far as limo fleets were concerned, Lincoln came up with an interesting answer: they took their new MKT crossover (a relation of the MKS) and created a variant specifically for fleets that they labelled the new "Town Car". Many of these can now be seen in livery service as black cars, and a few (like the one on the left in this photo) have been converted and offered to limo operators.
I'm not terribly convinced - the MKT simply doesn't seem like true Town Car to me. The MKS is more worthy a successor, but it still doesn't quite get to where I'd like a true Town Car successor to be.
The old Town Car will be sorely missed for some time to come, in my opinion. There's just nothing quite like it out there today.