Ala Dan,
I've only spoken to the folks at S&W about the various Walther product line, and the versions Walther licensed S&W to produce, as I've needed to ... which isn't very often.
I've known the occasional person that owned an American made PPK/S which functioned with just about any ammunition they used ... but those folks were in the minority, unfortunately.
Funny you should mention the addition of a slide stop, though, one which could be externally activated, being incorporated in the American produced PPK & PPK/S.
Before the S&W version was released, I was told by someone from S&W that the idea of incorporating such a slide stop had already been discussed, and might be further explored at some point down the road. I'm sure that licensing agreements and all of the involved legal considerations revolving around the design would have to be explored and resolved, as well. Although the Walther PPK series hasn't ever interested me (it doesn't fit my hands well, and I dislike the heavy triggers) I'd be sort of curious to see how they might manage to squeeze a slide stop lever in the frame.
Then, there's the potential market to consider, with all of the other .380's available, many of which are sufficiently reliable and affordable. As you mentioned with the Bersa, there's probably some growing consumer interest and competition in the "pocket pistol" market. R&D costs money, and that money has to be recovered at some point.
Of course, I'm sure the other thing to consider is that with the wealth of smaller 9mm pistols entering the market, there's some competition regarding the calibers available in similar size pistol platforms.
Your thread topic has made me curious, however, and I'm going to try and remember to ask about this the next time I have occasion to talk to someone at the factory.
By the way, the new Walther product that REALLY interests me is the G22 bullpup .22 rifle. From what I've been told, this is going to be an outstanding semiauto .22 rifle, and will be fully supported with all manner of accessories.
Best always,
fb