They don't have the old molds anymore. They could theoretically create new ones, but why? The updated ponies are doing VERY VERY well so I don't see any need.
Plus there were so MANY ponies, so not EVERYONE walking through a store would find a pony that looked EXACTLY like their favorite childhood one - that's a lot of ponies to make the EXACT favourite.
And that's simply not economical, nor what they aimed to do, or else we wouldn't have G3s - we'd just see a rereleasing of the old ponies. (And what's the point of doing that, anyway? I have most of the original ponies. I don't need them.)
It would be cool to see them take cues from some of the old poses, though. The Twilight pegasus pose is one of my favourites, I'd love to see the G3 pegs in a similar pose.
I'd like to see some of the G2s done as G3s. I'm working on a G3 Sky Skimmer custom, but there were a few beautiful colour schemes that I just loved, like MoonShadow.