Jim,
Your suggestion to drop in a functional, tested, calibrated movement rather that servicing and returning the original movement would certainly shorten wait times for those calibers available, but I foresee some issues.
(A) Inspection. Some inspection would still be necessary to ensure that the movement sent in had not been altered or damaged, but this would take no longer than current inspection time.
(B) Warranty. Implementing this idea would impact warranties. Would all but the movement carry the date of sale warranty, while a replacement movement would carry a warranty from time of replacement? That's not too dissimilar from a service warranty and might work out.
(C) Concern for originality. For a brand for which originality, tradition, history, and completeness are important to many owners, this seems to me to pose the greatest barrier to implementing your idea, as illustrated in the anecdote below.
In the early years of Richard Mille production, I accompanied a friend whose RM005 FM stopped working to Beverly Hills, where service was said to be available. The watch was gone for less than 8 hours while we shopped and had lunch. When a fully functioning watch was returned to him the same day, we asked how this was possible and were told, "Simple. We keep a supply of Voucher movements on hand and just dropped in a different movement."
This was the most convenient service experience imaginable and the quickest turnaround I've ever encountered, but it left me thinking that the watch was a soulless piece of junk, and I lost all interest in the brand. It had the same effect on my friend, who traded the watch away at the next opportunity.
Efficiency is not the only value at play in servicing watches, and for Patek Philippe buyers, particularly those who bond with individual watches and their history, there is an emotional attachment that could be destroyed by a change to the proposed service model, to the detriment of the brand. I'd rather wait until they serviced my watch the way they've always done it.
Park