The inline from the beginning was designed to be very flexible. flexible enough to make the I-4 and 1-5 using the same tooling.

Many feel that ford missed the boat when GM released the the new Vortec 4200 I6, It may be posible  to make a 2.7-3.5l I-6
out of the Inline's tooling and sharing parts with the I-4 and I-5. Ford could place this engine in vehicles from Jaguars to Linclons, and offer a compact I-6 to compete with BMW and Lexus.  It woyuld be nice to have a I-6 for trucks too.

If you don't already know, I don't work for Ford so this may not be possible, but if they can make V-10s out V-8s and V-12s out of two V-6s, dammit It ought to be possible to make I-6 and even I-8s out of the inline.   

No plans for a I-6 yet but I hope they are looking into it.