Yes, I think I got now 
You are of course aware of this little guy? 
It toggles complete playback of sample, using the slice only as an offset.
The only practical difference between using this feature and what you suggest - sans stretch - is that, in your suggestion, there is a predefined duration for the slice.
Edit: I guess having the ability to “slip” content for any given slice is sort-of related to your other suggestion?