I'd say just go and buy one for Zelda.
There are some pretty good games on the horizon for the 3DS, and there will be a few more years of new 3DS games and content.
Might aswell buy one now rather than wait 3 years then regret buying one earlier. (Nintendo don't really like price-dropping by the way.)
As far as hacks go, I also reckon this thing will be uncrackable.
Yes like you said nothing is truly unhackable in a way, but consider the PS3, the hackers needed strong motivation before it was hacked.
No one really seems motivated at all to hack the 3DS right now, in my opinion.
You can however run regular DS flash carts in DS mode to play the old DS games,
but the pixel ratio is off so the games look pretty poor on the 3DS's screen.
Also, if the PSP is anything to go by, the oldest model version of the device will be the easiest to hack.
They may release tweaked versions of the 3DS which aren't hackable. (pretty much all consoles do this, sometimes before we even find the exploits.)
So that's another reason to get one earlier, especially if you want to get one to eventually hack it.