there is a market for providing extendable versions to aftermarket converters, I believe Cadillac does that with XTS.- maybe Lincoln too with MKS or MKT.
Lincoln has two versions of the MKT designed specifically for the taxi/livery market. IIRC, one basically has a taxi/livery-ready wiring harness, but the other is prepped for being extended. As I understand it, they've not gone over very well with the livery operators. It might help if there were a similar program for the MKS, but there's not.