I take it a compression lock would increase the price point appreciably? If not, that would improve an already-reliable lock, plus add a liner. But probably not worth it if it raises the price point. It might also be "too unfamiliar" for the general ELU.
RE handles: Perhaps it would be possible to redesign the mold to create more rounded, contoured scales instead of the "classic" boxier design? Also, would it be possible to mold a sandy texture into the FRN? Finally, perhaps better quality FRN is being produced now, with higher glass content to stiffen without becoming brittle? I think a harder, stronger FRN would be immediately noticeable in-hand. Chris Reeve apparently worked with Crucible in producing S30V; would Spyderco be able to work with a company to produce a better FRN? Doing so, then renaming it something other than FRN, Zytel, "plastic" could change user perceptions of the material's qualities -- among general users and knifeknuts. Maybe call it "tempered glass," "superglass," "glass composite," or something similar. (Trust me, we'll fall for it .)
RE full flat grind: I doubt we'll see it -- Sal, in the past, has noted that it doesn't appeal visually to the general (non-knifeknut) user, while the sabre-grind does. This is main reason, IIRC, that the Calypso Jr -- directly superior to the Delica from a performance standpoint -- didn't fly with the general public. FWIW, I think the Endura/Delica's edge grind is very versatile and easy to maintain.
Only two blade changes I could see would be 1) to add traction grooves behind the Spydie hole. And 2) to beef up the tip a little on the Endura by slightly modifying the tip grind, perhaps convexing it if that can be done without raising the price point? (It would be a significant improvement that appears minor; and folks just won't pay more for a "minor" upgrade.) Doing so would certainly enhance the Endura's "workhorse" status. Of course, leave the Delica tip as-is; a fine working tip is the whole point of going with a modified clip pt. instead of a drop pt., after all. Any blade style is a compromise, and everyone accepts that.
In other words: keep the blade the same (mostly or completely), and work on redesigning the handles.

In any case, I think the Endura/Delica line rocks -- a classic design, for sure.
2¢ --
Glen