My ideal Spyderco would be what James Mattis used to call a sport-utility knife: form factor and weight ideal for everyday carry, but within that limitation suitable for rough use, and backup defensive use. To that end, I'd like to see:
Blade:
- 3.5" -- this is big enough for any use, but not too unwieldy. And this is also dictated by the form factor: a 4.5" handle is suitable for comfortable carry by most everyone. Once you start getting to 4" blades and 5" handles, not everyone can carry them comfortably.
- VG-10 -- easily my fave of spyderco's current steels. If we open this up to any steel, I'd lean towards uncoated D-2.
- shape -- I waffle on this, because there are so many useful shapes. I might be happiest with something like the Starmate's blade, though my fave shape is a long straight clip. The Goddard is probably my very fave shape.
- Full flat grind -- I want performance out of this thing, and the Military and Calypso prove hands-down which way to go for all-around performance.
Lock: Compression lock. Is there any other?

Maybe nested to whatever extent possible, to keep the thickness down (carryability again).
Handle: G-10 is fine. Maybe a fancier version with carbon fibre, or even that fancy new colored carbon fibre. I'd just as soon stick with G-10 to keep costs down. 4.5" length at most. Ergonomic and secure, but useable with multiple hand positions. Again, I really like the Goddard's handle, but spyderco has many good all-around handles, like the endura's and calypso's.
Miscellaneous: high-mounted clip for deep pocket carry, I prefer tip-up but am mostly ambivalent, grooved thumb ramp on the blade
not on the handle.
Joe