Here is my left handed perspective
While I would love to have Spyderco put holes for left handed carry on all of their models. There are some models where it would just look horrible. The majority of knife buyers will purchase a knife based on appearance alone (only us knife knuts care about the other stuff).
Some models it suits very well, the new Adventura looks better, in my opinion, with all the holes drilled in it. It suits the knife. The new Delica and Endura, also looks good with it.
Holes on a Kopa? Please don't, it would detract from the elegance of the knife. Holes on a Persian? Wouldn't look as nice. (I did it anyway, but I own the knife, and that's my decision)
For heavy duty, hard use knives, like the Manix, Chinook II, and for lower price point knives, like the Delica and Endura, it makes sense.
But for the upscale models, I don't think it's economical for Spyderco to drill every model just to satisfy the small amount of ELUs who are left handed. In the worst case scenario, those extra holes may prevent other ELUs from buying one, simply because they believe it to be ugly. Is it worth it for Sypderco to gain a few left handed/ambi customers at the expense of several dozen right handed buyers?
I am left handed, and it's a pain in the butt to find good left handed knives, but I must commend Spyderco for offering as many as they do. Even the ones they don't can easily be drilled for ambi carry should the user so desire(something I'm actually having done right now).
Relatively speaking, Spyderco is one of the better companies with regard to ambi designs.
If Sal chooses to add more ambi designs in the future, I will happily purchase them, but I'm happy with what they offer now.
Just my opinion of course.