The company I represent has purchased 4 new factories and runs 2 in China in an attempt to fix the JIT problems. They have been battling the change for about 10 years and still have not succeeded in my opinion.
The thing that many don't realize about JIT systems is that you need to have a system that is able to produce at a considerably higher volume than if you are stocking inventory to account for the spikes.
If producing to inventory, your system only needs to be able to produce at the average sales rate. It can just plug along and keep working on stock. With JIT, the system needs to be able to produce at a rate to meet your absolute PEAK demand. That demand can also increase at any time. Once a JIT system gets behind, it's basically screwed for days or weeks.
Did that inventory actually cost more than having to double the production capability? Not to mention the need for tons of part time/seasonal/temp workers to cover peak times? What about the cost of unhappy customers?
I am NOT a fan of JIT. IMHO, there needs to be a crossbreed system where inventory is kept on a limited basis to help pad the system and even the flow of production.
Sorry, back to the original topic...
I would suspect that Ford, like other manufacture's, just underestimate the need for all parts. It took weeks before I was able to get a simple fuel pump gasket when they replaced the valve cover gaskets. That was with help from Lincoln.
We know that production have 3.5 EB vehicles hasn't ceased. I suspect that, like my gasket issue, it's just that all production is going to meet the demand for new vehicles. It is probably more a sign of the popularity of the vehicles than the need for replacement motors.