I'm guessing here...
I think the original design lacked the safety - it's a double action pistol, after all, and there's no reason why a properly engineered, lightweight firing pin backed by a spring would present any sort of a drop hazard. I think that the safety was a very late addition, driven either by a regulation in some important market, or perhaps because of an ignition problem what required a heavier firing pin. Then I think they stuffed it into the rear sight like that to minimize the number of parts that would have to be changed.
This is purely speculative, a result of staring at the thing and trying to second-guess what they were thinking.
Nobody in the after-market sight business wants to assume the liability of replacing a safety feature, so that pretty much killed any hope of support for the P250 platform. Personally, I'm quite happy with the sights so it's not a problem for me, but I'm guessing you won't see any more designers embracing this approach.
Is the P250 the perfect gun? It's perfect for the niche _I_ have for it... a modern bulldog revolver, a small heavy, with windex-bottle simplicity. I hope the modular concept catches on, but we'll see.
Speaking of modularity, I've long argued that the world need a lightweight, pistol-caliber, double-action carbine for home defense use by non gun-enthusiasts. Something that is light and handy, recoils gently, hits hard enough to matter, is forgiving of a lack of trigger discipline, and has a manual of arms no more complex than a double action revolver. A P250 carbine could be an awesome thing.