No apologies necessary.
First - is a modular handgun necessary? Clearly it isn't. Despite the catchy name of 'Modular Handgun System', Glock was a finalist and doesn't have the SIG's chassis system. The APX was the only other entrant I can recall with a similar design. So I'm not even sure the Army was really looking for this 'feature' in the first place. To Joe's point, maybe it'll change how they do business. Perhaps not. I don't think any Generals are staying up late pondering the logistical possibilities offered by a 'Modular Handgun'. In the scheme of things, the pistol is the least important military weapon system, and I think General Milley's comments about the procurement process were spot on.
So what does the P320 design offer in this respect? Really, it comes down to the frame design. Now, even the Army has said that it expects 90% of personnel to use the 'medium' grip frame. This is why I said I don't see too much utility for the individual user; most will choose a grip frame and stick with it.
Now, the fact is that the grip frame is an entirely disposable item. I think that prevents some interesting options for an organization. I mentioned frame wear. Frames can get beat up and damaged - and not just aesthetically. Polymer will wear over time. Now we can just pop on a new one. Maybe some organizations will need different frame features in the future. We already see SIG marketing their 'X-Carry' frame for SOF use (no idea why the X-Carry isn't suitable for general use, but sure, whatever).
Is the FCU a disposable item too? Jon's observations about forward armorer support are interesting. Problematic gun? Just swap out the FCU? Obviously this is the registered part so you can't pitch in the trash like a grip frame, but perhaps you have a supply of spare FCUs and problems are resolved the depot level?
Again, I'm certainly not wedded to the concept - I'm just not ready to dismiss it entirely as a gimmick either. I think it does present some interesting options that could be attractive at the organizational level, and I'll break out the popcorn to watch it evolve.
SIG is marketing themselves as the 'modular' firearms company (MHS, MPX, MCX, etc). Time will tell if their strategy proves successful.
I still think the Army should have selected the Glock entry.