Interesting, that S&W sells only "hammerless" revolvers without the IL. As noted above, that is not entirely logical! But it means S&W must have some openness to the idea of change...
IL threads tend to get locked... but I'd like to add a new thought to the discussion. What if S&W got their "Saf-T-Lock" legacy staff to design and engineer a lock with an entry port on the front strap, behind the trigger guard? Many people -- me included -- don't like the aesthetics of the IL. It could be placed mostly out of sight.
The new design could also incorporate a failsafe design. There have been few reports of IL failures, but just enough -- apparently all with light weight revolvers -- to put the dread in potential buyers. And I've looked at the mechanism, and have to admit the little spring and lever are puny.
So a better design would be one that is both more reliable and hidden. Does anyone really lock their revolver? Not many, but there are times it might be worth doing (e.g., while storing the revolver, in cases where you are really unsure who might come upon it -- kids? a non-gun person?).
Anyway, not to tempt the "lock this thread" folks, and I admit IL threads get tiresome, but if we can't get S&W to go back, maybe they can go forward, and do a better hidden lock...