Tough (and dangerous) to mess with your bread and butter. But...better guard; slightly bigger lip and/or deeper finger hole, something that really locks the index finger from moving. The current guard is too much a gradual curve. Also some directional teeth on the hump (like a file), so the thumb can press forward hard without sliding. Maybe add a tiny bit of length to butt end of the handle, round the blade side, and use the extra length to add a bent over, tapered extension to the clip that would really lock it into the handle, for those who don't like the slight rotation of the clip. Sort of like a Gerber EZ-Out, but at the clip end, not side.
Perhaps for a variant, instead of a remodel, a slight bowie like curve from the hump to the point. I have a cheap Chinese Delica ripoff that I picked up at Big Lots (liquidation store) out of curiosity that is the POS that I expected, but has a subtle curve to the blade that is unexpectedly appealing. If I can get an image I will, or I'd happily mail the thing to Sal if he asks.
I like flat ground blades, too, but I'm not sure if it's appropriate for the Delica/Endura or not. I know I'd carry my Calypso, Jr. more if it was tip up carry. Maybe that's why it didn't sell that well.