My guess would be yes...this may be the end of the line. Being that the D4 has a keyboard, their is a lot more work in updating OTAs because of the key mapping. Devices like the Nexus line will probably get the updates being more like they are developer devices. With the hardware upgrades that are being put into these phones now, by next year when Jelly Bean is in full effect, the D4 will seem out dated and Key Lime Pie will be the new thing.
Honestly no one has a clue right now.....though I suspect JellyBean to be in the future for the Droid 4.
The big hurdle was going from 2.3.x to 4.0.x (Gingerbread to ICS). There were significant changes in the code and how things (hardware/drivers) interact between Gingerbread and ICS that pretty much required starting over from the beginning.
ICS to JB is a much smaller step (4.0.4 to 4.1.1). The code changes aren't as extreme and it should take a lot less time and be able to merge those changes in instead of starting completely over.
Will it happen...again no one knows...but I believe it will.